string number_format ( float number [, int decimal_places])
string number_format ( float number, int decimal_places, string decimal_point, string thousands_seperator)
Number_format() is a remarkably helpful function that takes a minimum of one parameter, the number to format, and returns that same number with grouped thousands. There are two function prototypes for number_format() as you either pass it one, two, or four parameters - passing it one or two fits the first prototype, and passing four fits the second.
So, if you pass number_format() a parameter of "1234567", it will return "1,234,567". By default, number_format() rounds fractions - 1234567.89 becomes 1,234,568. However, you can change this by specifying the second parameter, which is the number of decimal places to include. Parameter three allows you to choose the character to use as your decimal point, and parameter four allows you to choose the character to use as your thousands separator. Here is how it all looks in PHP:
$num = 12345.6789;
$a = number_format($num);
$b = number_format($num, 3);
$c = number_format($num, 4, ',', '.');
?>
After running that script, $a will be set to 12,346, $b will be set to 12,345.679, and $c will be set to 12.345,6789 (periods used to separate thousands, and commas used for the decimal point, east European-style).
As you can imagine, number_format() is incredibly useful when it comes to formatting money for checkout pages in shopping baskets, although it is useful anywhere you need to represent large numbers - adding a thousand separator invariably makes things easier to read.
Sunday, July 5, 2009
Wrapping your lines
string wordwrap ( string source [, int width [, string break [, boolean cut]]])
Although web pages wrap text automatically, there are two situations when you might want to wrap text yourself:
*
When printing to a console as opposed to a web page, text does not wrap automatically. Therefore, unless you want your users to scroll around a lot, it is best to wrap text for them.
*
When printing to a web page that has been designed to exactly accommodate a certain width of text, allowing browsers to wrap text whenever they want will likely lead to the design getting warped.
In either of these situations, the wordwrap() function comes to your aid. If you pass a sentence of text into wordwrap() with no other parameters, it will return that same string wrapped at the 75-character mark using "\n" for new lines. However, you can pass both the size and new line marker as parameters two and three if you want to, like this:
$text = "Word wrap will split this text up into smaller lines, which makes for easier reading and neater layout.";
$text = wordwrap($text, 20, "
");
print $text;
?>
Running that script will give you the following output:
Word wrap will split
this text up into
smaller lines, which
makes for easier
reading and neater
layout.
As you can see, wordwrap() has used
, a HTML new line marker, and split up words at the 20-character mark. Note that wordwrap() always pessimistically wraps words - that is, if you set the second parameter to 20, wordwrap() will always wrap when it hits 20 characters or under - not 21, 22, etc. The only exception to this is if you have words that are individually longer than 20 characters - wordwrap() will not break up a word, and so may return larger chunks than the limit you set.
If you really want your limit to be a hard maximum, you can supply 1 as a fourth parameter, which enables "cut" mode - words over the limit will be cut up if this is enabled. Here is an example of cut mode in action:
$text = "Micro-organism is a very long word.";
$text = wordwrap($text, 6, "\n", 1);
print $text;
?>
That will output the following:
Micro-
organi
sm is
a very
long
word.
Although web pages wrap text automatically, there are two situations when you might want to wrap text yourself:
*
When printing to a console as opposed to a web page, text does not wrap automatically. Therefore, unless you want your users to scroll around a lot, it is best to wrap text for them.
*
When printing to a web page that has been designed to exactly accommodate a certain width of text, allowing browsers to wrap text whenever they want will likely lead to the design getting warped.
In either of these situations, the wordwrap() function comes to your aid. If you pass a sentence of text into wordwrap() with no other parameters, it will return that same string wrapped at the 75-character mark using "\n" for new lines. However, you can pass both the size and new line marker as parameters two and three if you want to, like this:
$text = "Word wrap will split this text up into smaller lines, which makes for easier reading and neater layout.";
$text = wordwrap($text, 20, "
");
print $text;
?>
Running that script will give you the following output:
Word wrap will split
this text up into
smaller lines, which
makes for easier
reading and neater
layout.
As you can see, wordwrap() has used
, a HTML new line marker, and split up words at the 20-character mark. Note that wordwrap() always pessimistically wraps words - that is, if you set the second parameter to 20, wordwrap() will always wrap when it hits 20 characters or under - not 21, 22, etc. The only exception to this is if you have words that are individually longer than 20 characters - wordwrap() will not break up a word, and so may return larger chunks than the limit you set.
If you really want your limit to be a hard maximum, you can supply 1 as a fourth parameter, which enables "cut" mode - words over the limit will be cut up if this is enabled. Here is an example of cut mode in action:
$text = "Micro-organism is a very long word.";
$text = wordwrap($text, 6, "\n", 1);
print $text;
?>
That will output the following:
Micro-
organi
sm is
a very
long
word.
Finding a string within a string
Strpos(), and its case-insensitive sibling stripos(), returns the index of the first occurrence of a substring within a string. It is easier to explain in code, so here goes:
$string = "This is a strpos() test";
print strpos($string, "a") . "\n";
?>
That will return 8, because the first character in "This is a strpos() test" that is a lowercase A is at index 8. Remember that PHP considers the first letter of a string to be index 0, which means that the A strpos() found is actually the ninth character.
You can specify whole words in parameter two, which will make strpos() return the first position of that word within the string, for example strpos($string, "test") would return 19 - the index of the first letter in the matched word.
If the substring sent in parameter two is not found in parameter one, strpos() will return false. Consider this script:
$string = "This is a strpos() test";
$pos = strpos($string, "This");
if ($pos == false) {
print "Not found\n";
} else {
print "Found!\n";
}
?>
If you try executing that, you will find that it outputs "Not found", despite "This" quite clearly being in $string. Is it another case sensitivity problem? Not quite. This time the problem lies in the fact that "This" is the first thing in $string, which means that strpos() will return 0. However, PHP considers 0 to be the same value as false, which means that our if statement cannot tell the difference between "Substring not found" and "Substring found at index 0" - quite a problem!
Luckily, PHP comes to the rescue with the === operator, which, if you recall, means "is identical to", which means $pos must be equal to false and of the same type as false (boolean). If the "This" is found in $string, strpos()will return 0, but it will be of type integer . If we change our if statement to use === rather than ==, PHP will check the value of 0 and false and find they match (both false), then check the types of 0 and false, and find that they do not match - the former is an integer, and the latter is a boolean.
So, the corrected version of the script is this:
$string = "This is a strpos() test";
$pos = strpos($string, "This");
if ($pos === false) {
print "Not found\n";
} else {
print "Found!\n";
}
?>
Now, consider this next script, which tries to match the "i" in "is":
$string = "This is a strpos() test";
$pos = strpos($string, "i");
if ($pos === false) {
print "Not found\n";
} else {
print "Found at $pos!\n";
}
?>
The problem there is that strpos() matches the first "i" it comes across, which will be in "This". Fortunately there is a third parameter to strpos() that allows us to specify where to start from. As the "i" in "This" is at index 2, we just need to specify one place after that (3) as the start position for strpos(), and it will report back the next "i" after it. For example:
$string = "This is a strpos() test";
$pos = strpos($string, "i", 3);
if ($pos === false) {
print "Not found\n";
} else {
print "Found at $pos!\n";
}
?>
This time that will print "found at 5!", which is the position of the "i" in "is".
$string = "This is a strpos() test";
print strpos($string, "a") . "\n";
?>
That will return 8, because the first character in "This is a strpos() test" that is a lowercase A is at index 8. Remember that PHP considers the first letter of a string to be index 0, which means that the A strpos() found is actually the ninth character.
You can specify whole words in parameter two, which will make strpos() return the first position of that word within the string, for example strpos($string, "test") would return 19 - the index of the first letter in the matched word.
If the substring sent in parameter two is not found in parameter one, strpos() will return false. Consider this script:
$string = "This is a strpos() test";
$pos = strpos($string, "This");
if ($pos == false) {
print "Not found\n";
} else {
print "Found!\n";
}
?>
If you try executing that, you will find that it outputs "Not found", despite "This" quite clearly being in $string. Is it another case sensitivity problem? Not quite. This time the problem lies in the fact that "This" is the first thing in $string, which means that strpos() will return 0. However, PHP considers 0 to be the same value as false, which means that our if statement cannot tell the difference between "Substring not found" and "Substring found at index 0" - quite a problem!
Luckily, PHP comes to the rescue with the === operator, which, if you recall, means "is identical to", which means $pos must be equal to false and of the same type as false (boolean). If the "This" is found in $string, strpos()will return 0, but it will be of type integer . If we change our if statement to use === rather than ==, PHP will check the value of 0 and false and find they match (both false), then check the types of 0 and false, and find that they do not match - the former is an integer, and the latter is a boolean.
So, the corrected version of the script is this:
$string = "This is a strpos() test";
$pos = strpos($string, "This");
if ($pos === false) {
print "Not found\n";
} else {
print "Found!\n";
}
?>
Now, consider this next script, which tries to match the "i" in "is":
$string = "This is a strpos() test";
$pos = strpos($string, "i");
if ($pos === false) {
print "Not found\n";
} else {
print "Found at $pos!\n";
}
?>
The problem there is that strpos() matches the first "i" it comes across, which will be in "This". Fortunately there is a third parameter to strpos() that allows us to specify where to start from. As the "i" in "This" is at index 2, we just need to specify one place after that (3) as the start position for strpos(), and it will report back the next "i" after it. For example:
$string = "This is a strpos() test";
$pos = strpos($string, "i", 3);
if ($pos === false) {
print "Not found\n";
} else {
print "Found at $pos!\n";
}
?>
This time that will print "found at 5!", which is the position of the "i" in "is".
Padding out a string
string str_pad ( string input, int pad_length [, string pad_string [, int pad_type]])
Next up, str_pad() makes a given string (parameter one) larger by X number of characters (parameter two) by adding on spaces. For example:
$string = "Goodbye, Perl!";
$newstring = str_pad($string, 10);
?>
That code would leave " Goodbye, Perl! " in $newstring, which is the same string from $string except with five spaces on either side, equalling the 10 we passed in as parameter two.
Str_pad() has an optional third parameter that lets you set the padding character to use, so:
$string = "Goodbye, Perl!";>
$newstring = str_pad($string, 10, 'a');
?>
That would put "aaaaaGoodbye, Perl!aaaaa" into $newstring.
We can extend the function even more by using it is optional fourth parameter, which allows us to specify which side we want the padding added to. The fourth parameter is specified as a constant, and you either use STR_PAD_LEFT, STR_PAD_RIGHT, or STR_PAD_BOTH:
$string = "Goodbye, Perl!";
$a = str_pad($string, 10, '-', STR_PAD_LEFT);
$b = str_pad($string, 10, '-', STR_PAD_RIGHT);
$c = str_pad($string, 10, '-', STR_PAD_BOTH);
?>
That code will set $a to be "----------Goodbye, Perl!", $b to be "Goodbye, Perl!----------", and $c to be "-----Goodbye, Perl!-----", as expected.
Note that HTML only allows a maximum of one space at any time. If you want to pad more, you will need to use " ", the HTML code for non-breaking space.
Next up, str_pad() makes a given string (parameter one) larger by X number of characters (parameter two) by adding on spaces. For example:
$string = "Goodbye, Perl!";
$newstring = str_pad($string, 10);
?>
That code would leave " Goodbye, Perl! " in $newstring, which is the same string from $string except with five spaces on either side, equalling the 10 we passed in as parameter two.
Str_pad() has an optional third parameter that lets you set the padding character to use, so:
$string = "Goodbye, Perl!";>
$newstring = str_pad($string, 10, 'a');
?>
That would put "aaaaaGoodbye, Perl!aaaaa" into $newstring.
We can extend the function even more by using it is optional fourth parameter, which allows us to specify which side we want the padding added to. The fourth parameter is specified as a constant, and you either use STR_PAD_LEFT, STR_PAD_RIGHT, or STR_PAD_BOTH:
$string = "Goodbye, Perl!";
$a = str_pad($string, 10, '-', STR_PAD_LEFT);
$b = str_pad($string, 10, '-', STR_PAD_RIGHT);
$c = str_pad($string, 10, '-', STR_PAD_BOTH);
?>
That code will set $a to be "----------Goodbye, Perl!", $b to be "Goodbye, Perl!----------", and $c to be "-----Goodbye, Perl!-----", as expected.
Note that HTML only allows a maximum of one space at any time. If you want to pad more, you will need to use " ", the HTML code for non-breaking space.
Parsing a string into variables
void parse_str ( string input [, array store])
Previously we looked at a handful of the variables set for you inside the superglobal arrays, of which one was QUERY_STRING. If you recall, this is the literal text sent after the question mark in a HTTP GET request, which means that if the page requested was "mypage.php?foo=bar&bar=baz", QUERY_STRING is set to "foo=bar&bar=baz".
The parse_str() function is designed to take a query string like that one and convert it to variables in the same way that PHP does when variables come in. The difference is that variables parsed using parse_str() are converted to global variables, as opposed to elements inside $_GET. So:
if (isset($foo)) {
print "Foo is $foo
";
} else {
print "Foo is unset
";
}
parse_str("foo=bar&bar=baz");
if (isset($foo)) {
print "Foo is $foo
";
} else {
print "Foo is unset
";
}
?>
That will print out "Foo is unset" followed by "Foo is bar", because the call to parse_str() will set $foo to "bar" and $bar to "baz". Optionally, you can pass an array as the second parameter to parse_str(), and it will put the variables into there. That would make the script look like this:
$array = array();
if (isset($array['foo'])) {
print "Foo is {$array['foo']}
";
} else {
print "Foo is unset
";
}
parse_str("foo=bar&bar=baz", $array);
if (isset($array['foo'])) {
print "Foo is {$array['foo']}
";
} else {
print "Foo is unset
";
}
?>
That script outputs the same as before, except that the variables found in the query string are placed into $array. As you can see, the variable names are used as keys in the array and their values are used as the array values.
Previously we looked at a handful of the variables set for you inside the superglobal arrays, of which one was QUERY_STRING. If you recall, this is the literal text sent after the question mark in a HTTP GET request, which means that if the page requested was "mypage.php?foo=bar&bar=baz", QUERY_STRING is set to "foo=bar&bar=baz".
The parse_str() function is designed to take a query string like that one and convert it to variables in the same way that PHP does when variables come in. The difference is that variables parsed using parse_str() are converted to global variables, as opposed to elements inside $_GET. So:
if (isset($foo)) {
print "Foo is $foo
";
} else {
print "Foo is unset
";
}
parse_str("foo=bar&bar=baz");
if (isset($foo)) {
print "Foo is $foo
";
} else {
print "Foo is unset
";
}
?>
That will print out "Foo is unset" followed by "Foo is bar", because the call to parse_str() will set $foo to "bar" and $bar to "baz". Optionally, you can pass an array as the second parameter to parse_str(), and it will put the variables into there. That would make the script look like this:
$array = array();
if (isset($array['foo'])) {
print "Foo is {$array['foo']}
";
} else {
print "Foo is unset
";
}
parse_str("foo=bar&bar=baz", $array);
if (isset($array['foo'])) {
print "Foo is {$array['foo']}
";
} else {
print "Foo is unset
";
}
?>
That script outputs the same as before, except that the variables found in the query string are placed into $array. As you can see, the variable names are used as keys in the array and their values are used as the array values.
Regular expression syntax examples
In order to give you a quick reference to the different patterns and what they will match, here's a comprehensive table of all we've covered. Column one contains example expressions, and column two contains what that expression will match.
Expr
Will match...
foo
the string "foo"
^foo
"foo" at the start of a line
foo$
"foo" at the end of a line
^foo$
"foo" when it is alone on a line
[Ff]oo
"Foo" or "foo"
[abc]
a, b, or c
[^abc]
d, e, f, g, h, etc - everything that is not a, b, or c (^ is "not" inside sets)
[A-Z]
any uppercase letter
[a-z]
any lowercase letter
[A-Za-z]
any letter
[A-Za-z0-9]
any letter of number
[A-Z]+
one or more uppercase letters
[A-Z]*
zero or more uppercase letters
[A-Z]?
zero or one uppercase letters
[A-Z]{3}
3 uppercase letters
[A-Z]{3,}
a minimum of 3 uppercase letters
[A-Z]{1,3}
1-3 uppercase letters
[^0-9]
any non-numeric character
[^0-9A-Za-z]
any symbol (not a number or a letter)
Fo*
F, Fo, Foo, Fooo, Foooo, etc
Fo+
Fo, Foo, Fooo, Foooo, etc
Fo?
F, Fo
.
any character except \n (new line)
\b
a word boundary. E.g. te\b matches the "te" in "late", but not the "te" in "tell".
\B
a non-word boundary. "te\B" matches the "te" in "tell" but not the "te" in "late".
\n
new line character
\s
any whitespace (new line, space, tab, etc)
\S
any non-whitespace character
Expr
Will match...
foo
the string "foo"
^foo
"foo" at the start of a line
foo$
"foo" at the end of a line
^foo$
"foo" when it is alone on a line
[Ff]oo
"Foo" or "foo"
[abc]
a, b, or c
[^abc]
d, e, f, g, h, etc - everything that is not a, b, or c (^ is "not" inside sets)
[A-Z]
any uppercase letter
[a-z]
any lowercase letter
[A-Za-z]
any letter
[A-Za-z0-9]
any letter of number
[A-Z]+
one or more uppercase letters
[A-Z]*
zero or more uppercase letters
[A-Z]?
zero or one uppercase letters
[A-Z]{3}
3 uppercase letters
[A-Z]{3,}
a minimum of 3 uppercase letters
[A-Z]{1,3}
1-3 uppercase letters
[^0-9]
any non-numeric character
[^0-9A-Za-z]
any symbol (not a number or a letter)
Fo*
F, Fo, Foo, Fooo, Foooo, etc
Fo+
Fo, Foo, Fooo, Foooo, etc
Fo?
F, Fo
.
any character except \n (new line)
\b
a word boundary. E.g. te\b matches the "te" in "late", but not the "te" in "tell".
\B
a non-word boundary. "te\B" matches the "te" in "tell" but not the "te" in "late".
\n
new line character
\s
any whitespace (new line, space, tab, etc)
\S
any non-whitespace character
Checking whether a function is available
bool function_exists ( string function_name)
If you're working with functions that are not part of the core of PHP, that is, functions that are from an extension that needs to be enabled by users, it's a smart move to use the function_exists() function. This takes a function name as its only parameter, and returns true if that function (either built-in, or one you've defined yourself) is available for use. Note that it only checks whether the function is available, not whether it will work - your system may not be configured properly for some functions.
Author's Note: If you ever want to know whether you have a function available to you, use the function_exists() function. This takes one string parameter that is the name of a function, and returns true if the function exists or false if it does not. Many people use function_exists() to find out whether they have an extension available, by calling function_exists() on a function of that extension. However, this is accomplished much more easily with the function extension_loaded() function covered later.
If you're working with functions that are not part of the core of PHP, that is, functions that are from an extension that needs to be enabled by users, it's a smart move to use the function_exists() function. This takes a function name as its only parameter, and returns true if that function (either built-in, or one you've defined yourself) is available for use. Note that it only checks whether the function is available, not whether it will work - your system may not be configured properly for some functions.
Author's Note: If you ever want to know whether you have a function available to you, use the function_exists() function. This takes one string parameter that is the name of a function, and returns true if the function exists or false if it does not. Many people use function_exists() to find out whether they have an extension available, by calling function_exists() on a function of that extension. However, this is accomplished much more easily with the function extension_loaded() function covered later.
Changing string case
string strtoupper ( string source)
string strtolower ( string source)
string ucfirst ( string source)
string ucwords ( string source)
Strtoupper() is part of a small family of functions that affect the case of characters of strings. Strtoupper() takes one string parameter, and returns that string entirely in uppercase. Other variations include strtolower(), to convert the string to lowercase, ucfirst() to convert the first letter of every string to uppercase, and ucwords(), to convert the first letter of every word in the string to uppercase. They all take one parameter and return the converted result, so once you learn one you have learnt them all:
$string = "i like to program in PHP";
$a = strtoupper($string);
$b = strtolower($string);
$c = ucfirst($string);
$d = ucwords($string);
$e = ucwords(strtolower($string));
?>
Each of those variables get set to a slightly different value: $a becomes "I LIKE TO PROGAM IN PHP", $b becomes "i like to program in php", $c becomes "I like to program in PHP", $d becomes "I Like To Program In PHP", and $e becomes "I Like To Program In Php".
From that, you should be able to see that in calls such as ucwords(), PHP will not change existing capital letters to lowercase, which is why $d and $e are different - for $e, all the letters are lowercased first, then passed through ucwords() to make PHP into Php.
string strtoupper ( string source)
string strtolower ( string source)
string ucfirst ( string source)
string ucwords ( string source)
Strtoupper() is part of a small family of functions that affect the case of characters of strings. Strtoupper() takes one string parameter, and returns that string entirely in uppercase. Other variations include strtolower(), to convert the string to lowercase, ucfirst() to convert the first letter of every string to uppercase, and ucwords(), to convert the first letter of every word in the string to uppercase. They all take one parameter and return the converted result, so once you learn one you have learnt them all:
$string = "i like to program in PHP";
$a = strtoupper($string);
$b = strtolower($string);
$c = ucfirst($string);
$d = ucwords($string);
$e = ucwords(strtolower($string));
?>
Each of those variables get set to a slightly different value: $a becomes "I LIKE TO PROGAM IN PHP", $b becomes "i like to program in php", $c becomes "I like to program in PHP", $d becomes "I Like To Program In PHP", and $e becomes "I Like To Program In Php".
From that, you should be able to see that in calls such as ucwords(), PHP will not change existing capital letters to lowercase, which is why $d and $e are different - for $e, all the letters are lowercased first, then passed through ucwords() to make PHP into Php.
string strtolower ( string source)
string ucfirst ( string source)
string ucwords ( string source)
Strtoupper() is part of a small family of functions that affect the case of characters of strings. Strtoupper() takes one string parameter, and returns that string entirely in uppercase. Other variations include strtolower(), to convert the string to lowercase, ucfirst() to convert the first letter of every string to uppercase, and ucwords(), to convert the first letter of every word in the string to uppercase. They all take one parameter and return the converted result, so once you learn one you have learnt them all:
$string = "i like to program in PHP";
$a = strtoupper($string);
$b = strtolower($string);
$c = ucfirst($string);
$d = ucwords($string);
$e = ucwords(strtolower($string));
?>
Each of those variables get set to a slightly different value: $a becomes "I LIKE TO PROGAM IN PHP", $b becomes "i like to program in php", $c becomes "I like to program in PHP", $d becomes "I Like To Program In PHP", and $e becomes "I Like To Program In Php".
From that, you should be able to see that in calls such as ucwords(), PHP will not change existing capital letters to lowercase, which is why $d and $e are different - for $e, all the letters are lowercased first, then passed through ucwords() to make PHP into Php.
string strtoupper ( string source)
string strtolower ( string source)
string ucfirst ( string source)
string ucwords ( string source)
Strtoupper() is part of a small family of functions that affect the case of characters of strings. Strtoupper() takes one string parameter, and returns that string entirely in uppercase. Other variations include strtolower(), to convert the string to lowercase, ucfirst() to convert the first letter of every string to uppercase, and ucwords(), to convert the first letter of every word in the string to uppercase. They all take one parameter and return the converted result, so once you learn one you have learnt them all:
$string = "i like to program in PHP";
$a = strtoupper($string);
$b = strtolower($string);
$c = ucfirst($string);
$d = ucwords($string);
$e = ucwords(strtolower($string));
?>
Each of those variables get set to a slightly different value: $a becomes "I LIKE TO PROGAM IN PHP", $b becomes "i like to program in php", $c becomes "I like to program in PHP", $d becomes "I Like To Program In PHP", and $e becomes "I Like To Program In Php".
From that, you should be able to see that in calls such as ucwords(), PHP will not change existing capital letters to lowercase, which is why $d and $e are different - for $e, all the letters are lowercased first, then passed through ucwords() to make PHP into Php.
Trimming whitespace
string trim ( string source [, string charlist])
string ltrim ( string source [, string charlist])
string rtrim ( string source [, string charlist])
Trim() is a function to strip whitespace from either side of a string variable, with "whitespace" meaning spaces, new lines, and tabs. That is, if you have the string " This is a test " and pass it to trim() as its first parameter, it will return the string "This is a test" - the same thing, but with the spaces trimmed off the end.
You can pass an optional second parameter to trim() if you want, which should be a string specifying the characters you want it to trim(). For example, if we were to pass to trim the second parameter " tes" (that starts with a space), it would output "This is a" - the test would be trimmed, as well as the spaces. As you can see, trim() is again case sensitive - the T in "This" is left untouched.
Trim() has two minor variant functions, ltrim() and rtrim(), which do the same thing but only trim from the left and right respectively.
Here are some examples:
$a = trim(" testing ");
$b = trim(" testing ", " teng");
$c = ltrim(" testing ");
?>
$a will result in "testing", $b will result in "sti", and $c will result in "testing " - as expected, and not surprising because trim() et al are simple to use.
string ltrim ( string source [, string charlist])
string rtrim ( string source [, string charlist])
Trim() is a function to strip whitespace from either side of a string variable, with "whitespace" meaning spaces, new lines, and tabs. That is, if you have the string " This is a test " and pass it to trim() as its first parameter, it will return the string "This is a test" - the same thing, but with the spaces trimmed off the end.
You can pass an optional second parameter to trim() if you want, which should be a string specifying the characters you want it to trim(). For example, if we were to pass to trim the second parameter " tes" (that starts with a space), it would output "This is a" - the test would be trimmed, as well as the spaces. As you can see, trim() is again case sensitive - the T in "This" is left untouched.
Trim() has two minor variant functions, ltrim() and rtrim(), which do the same thing but only trim from the left and right respectively.
Here are some examples:
$a = trim(" testing ");
$b = trim(" testing ", " teng");
$c = ltrim(" testing ");
?>
$a will result in "testing", $b will result in "sti", and $c will result in "testing " - as expected, and not surprising because trim() et al are simple to use.
Return values
You're allowed to return one and only one value back from functions, and you do this by using the return statement. In our example, we could have used "return 'foo';" or "return 10 + 10;" to pass other values back, but "return 1;" is easiest, and usually the most common as it is the same as "return true;"
You can return any variable you want, as long as it is just one variable - it can be an integer, a string, a database connection, etc. The "return" keyword sets up the function return value to be whatever variable you use with it, then exits the function immediately. You can also just use "return;", which means "exit without sending a value back."
Consider this script:
function foo() {
print "In function";
return 1;
print "Leaving function...";
}
print foo();
?>
That will output "In function", followed by "1", and then the script will terminate. The reason we never see "Leaving function..." is because the line "return 1" passes one back then immediately exits - the second print statement in foo() is never reached.
If you want to pass more than one value back, you need to use an array - this is covered soon.
A popular thing to do is to return the value of a conditional statement, e.g.:
return $i > 10;
If $i is indeed greater than 10, the > operator will return 1, so it is the same as having "return 1", but if $i is less than or equal to ten, it is the same as being "return 0".
You can return any variable you want, as long as it is just one variable - it can be an integer, a string, a database connection, etc. The "return" keyword sets up the function return value to be whatever variable you use with it, then exits the function immediately. You can also just use "return;", which means "exit without sending a value back."
Consider this script:
function foo() {
print "In function";
return 1;
print "Leaving function...";
}
print foo();
?>
That will output "In function", followed by "1", and then the script will terminate. The reason we never see "Leaving function..." is because the line "return 1" passes one back then immediately exits - the second print statement in foo() is never reached.
If you want to pass more than one value back, you need to use an array - this is covered soon.
A popular thing to do is to return the value of a conditional statement, e.g.:
return $i > 10;
If $i is indeed greater than 10, the > operator will return 1, so it is the same as having "return 1", but if $i is less than or equal to ten, it is the same as being "return 0".
Variable functions
bool is_callable ( mixed function_name [, bool syntax_only [, string callable_name]])
mixed call_user_func ( callback function [, mixed parameter [, mixed ...]])
mixed call_user_func_array ( callback function [, array parameters])
As you have seen already, PHP has variable variables so it is not surprising we have variable functions. This particular piece of clever functionality allows you to write code like this:
$func = "sqrt";
print $func(49);
?>
PHP sees that you are calling a function using a variable, looks up the value of the variable, then calls the matching function. The code above will therefore return 7 - the square root of 49.
As variable functions are quite unusual and also easy to get wrong, there is a special PHP function, is_callable(), that takes a string as its only parameter and returns true if that string contains a function name that can be called using a variable function. Thus, our script becomes this:
$func = "sqrt";
if (is_callable($func)) {
print $func(49);
}
?>
As an alternative to variable functions, you can use call_user_func() and call_user_func_array(), which take the function to call as their first parameter. The difference between the two is that call_user_func() takes the parameters to pass into the variable function as multiple parameters to itself, whereas call_user_func_array() takes an array of parameters as its second parameter.
This next script demonstrates both of these two performing a functionally similar operation, replacing "monkeys" with "giraffes" in a sentence using str_replace():
$func = "str_replace";
$output_single = call_user_func($func, "monkeys", "giraffes", "Hundreds and thousands of monkeys\n");
$params = array("monkeys", "giraffes", "Hundreds and thousands of monkeys\n");
$output_array = call_user_func_array($func, $params);
echo $output_single;
echo $output_array;
?>
Although call_user_func() is essentially the same as using a variable function, call_user_func_array() is very helpful for functions that have complex and variable parameter requirements. One popular application for variable functions is to allow other developers using your code to register callbacks - they pass in the name of the function they want your code to call, then you can use call_user_func() to execute that.
mixed call_user_func ( callback function [, mixed parameter [, mixed ...]])
mixed call_user_func_array ( callback function [, array parameters])
As you have seen already, PHP has variable variables so it is not surprising we have variable functions. This particular piece of clever functionality allows you to write code like this:
$func = "sqrt";
print $func(49);
?>
PHP sees that you are calling a function using a variable, looks up the value of the variable, then calls the matching function. The code above will therefore return 7 - the square root of 49.
As variable functions are quite unusual and also easy to get wrong, there is a special PHP function, is_callable(), that takes a string as its only parameter and returns true if that string contains a function name that can be called using a variable function. Thus, our script becomes this:
$func = "sqrt";
if (is_callable($func)) {
print $func(49);
}
?>
As an alternative to variable functions, you can use call_user_func() and call_user_func_array(), which take the function to call as their first parameter. The difference between the two is that call_user_func() takes the parameters to pass into the variable function as multiple parameters to itself, whereas call_user_func_array() takes an array of parameters as its second parameter.
This next script demonstrates both of these two performing a functionally similar operation, replacing "monkeys" with "giraffes" in a sentence using str_replace():
$func = "str_replace";
$output_single = call_user_func($func, "monkeys", "giraffes", "Hundreds and thousands of monkeys\n");
$params = array("monkeys", "giraffes", "Hundreds and thousands of monkeys\n");
$output_array = call_user_func_array($func, $params);
echo $output_single;
echo $output_array;
?>
Although call_user_func() is essentially the same as using a variable function, call_user_func_array() is very helpful for functions that have complex and variable parameter requirements. One popular application for variable functions is to allow other developers using your code to register callbacks - they pass in the name of the function they want your code to call, then you can use call_user_func() to execute that.
Overriding scope with the GLOBALS array
At some point in your PHP programming career you will want to read a global variable inside a function - I can pretty much guarantee that, because it is a very popular thing to do. Luckily, it is made easy for you by PHP through the $GLOBALS superglobal array, which allows you to access global variables even from within functions. When it comes to the $GLOBALS array it is quite simple: all variables declared in the global scope are in the $GLOBALS array, which you can access anywhere in the script.
To demonstrate this in action, consider the following script:
function foo() {
$GLOBALS['bar'] = "wombat";
}
$bar = "baz";
foo();
print $bar;
?>
What do you think that will output this time? If you guessed "wombat", you would be correct - the foo() function literally alters a variable outside of its scope, so that even after it returns control back to the main script, its effect is still felt. You can of course read variables in the same way, like this:
$localbar = $GLOBALS['bar'];
However, that is quite hard on the eyes. PHP allows you to use a special keyword, GLOBAL, to allow a variable to be accessed locally. For example:
function myfunc() {
GLOBAL $foo, $bar, $baz;
++$baz;
}
That would allow a function to read the global variables $foo, $bar, and $baz. The ++$baz line will increment $baz by 1, and this will be reflected in the global scope also.
To demonstrate this in action, consider the following script:
function foo() {
$GLOBALS['bar'] = "wombat";
}
$bar = "baz";
foo();
print $bar;
?>
What do you think that will output this time? If you guessed "wombat", you would be correct - the foo() function literally alters a variable outside of its scope, so that even after it returns control back to the main script, its effect is still felt. You can of course read variables in the same way, like this:
$localbar = $GLOBALS['bar'];
However, that is quite hard on the eyes. PHP allows you to use a special keyword, GLOBAL, to allow a variable to be accessed locally. For example:
function myfunc() {
GLOBAL $foo, $bar, $baz;
++$baz;
}
That would allow a function to read the global variables $foo, $bar, and $baz. The ++$baz line will increment $baz by 1, and this will be reflected in the global scope also.
Variable scope in functions
As mentioned already, variables declared outside of functions and classes are considered "global" - generally available to the script. However, as functions are independent blocks, their variables are self-contained and do not affect variables in the main script. In the same way, variables from the main script are not implicitly made available inside functions. Take a look at this example script:
function foo() {
$bar = "wombat";
}
$bar = "baz";
foo();
print $bar;
?>
Execution of the script starts at the $bar = "baz" line, and then calls the foo() function. Now, as you can see, foo() sets $bar to "wombat", then returns control to the main script where $bar is printed out. Consider for a moment what you think that script will do, taking into account what I have just said regarding variable scope in functions.
There are, overall, three possibilities:
1.
The script will print "baz"
2.
The script will print "wombat"
3.
The script will print nothing
Possibility one would be the case if the $bar variable was set outside of the function, foo() was called and set its own, local version of $bar, which was deleted once the function ended, leaving the original $bar in place.
Possibility two would be the case if the $bar variable was set outside of the function, foo() was called, and changed the global copy of $bar, therefore printing out the new value once control returns to the main script.
Possibility three would be the case if variables are lost in between function calls.
It is quite simple to discount the third possibility - variables declared globally, that is, outside of functions, remain in the global scope, no matter what functions you call.
The second possibility would mean that variables declared globally are automatically made available inside functions, which we know is not the case. Therefore, the first possibility is in fact correct - foo() is called, and, having no knowledge that a $bar variable exists in the global scope, creates a $bar variable in its local scope. Once the function ends, all local scopes are tossed away, leaving the original $bar variable intact.
For many this procedure is second nature, however it does take a little getting used to if you are new to programming, which is why I have gone into so much depth. This explicit level of scope is something you will find is particularly important once you go beyond simple scripts.
function foo() {
$bar = "wombat";
}
$bar = "baz";
foo();
print $bar;
?>
Execution of the script starts at the $bar = "baz" line, and then calls the foo() function. Now, as you can see, foo() sets $bar to "wombat", then returns control to the main script where $bar is printed out. Consider for a moment what you think that script will do, taking into account what I have just said regarding variable scope in functions.
There are, overall, three possibilities:
1.
The script will print "baz"
2.
The script will print "wombat"
3.
The script will print nothing
Possibility one would be the case if the $bar variable was set outside of the function, foo() was called and set its own, local version of $bar, which was deleted once the function ended, leaving the original $bar in place.
Possibility two would be the case if the $bar variable was set outside of the function, foo() was called, and changed the global copy of $bar, therefore printing out the new value once control returns to the main script.
Possibility three would be the case if variables are lost in between function calls.
It is quite simple to discount the third possibility - variables declared globally, that is, outside of functions, remain in the global scope, no matter what functions you call.
The second possibility would mean that variables declared globally are automatically made available inside functions, which we know is not the case. Therefore, the first possibility is in fact correct - foo() is called, and, having no knowledge that a $bar variable exists in the global scope, creates a $bar variable in its local scope. Once the function ends, all local scopes are tossed away, leaving the original $bar variable intact.
For many this procedure is second nature, however it does take a little getting used to if you are new to programming, which is why I have gone into so much depth. This explicit level of scope is something you will find is particularly important once you go beyond simple scripts.
Variable parameter counts
int func_num_args ( )
mixed func_get_arg ( int arg_num)
array func_get_args ( )
The printf() function we examined previously is able to take an arbitrary number of parameters. That is, it could take just one parameter, or five, or fifty, or five hundred - it can take as many as are passed into it by the user. This is known as a variable-length parameter list, and it is automatically implemented in your user functions. For example:
function some_func($a, $b) {
$j = 1;
}
some_func(1,2,3,4,5,6,7,8);
?>
Here the function some_func() is defined to only take two parameters, $a and $b, but we call it with eight parameters and the script should run without a problem. In that example, 1 will be placed into $a, and 2 will be placed into $b, but what happens to the other parameters?
Coming to your rescue are three functions: func_num_args(), func_get_arg(), and func_get_args(), of which the first and last take no parameters. To get the number of arguments that were passed into your function, call func_num_args() and read its return value. To get the value of an individual parameter, use func_get_arg() and pass in the parameter number you want to retrieve to have its value returned back to you. Finally, func_get_args() returns an array of the parameters that were passed in. Here's an example:
function some_func($a, $b) {
for ($i = 0; $i < func_num_args(); ++$i) {
$param = func_get_arg($i);
echo "Received parameter $param.\n";
}
}
function some_other_func($a, $b) {
$param = func_get_args();
$param = join(", ", $param);
echo "Received parameters: $param.\n";
}
some_func(1,2,3,4,5,6,7,8);
some_other_func(1,2,3,4,5,6,7,8);
?>
Using func_num_args() alone you can easily implement function error checking. You can, for example, start off each of your functions by checking to make sure func_num_args() is what you are expecting, and, if not, exit. Once you add func_get_arg() into the mix, however, you should easily be able to create your own functions that work with any number of parameters.
mixed func_get_arg ( int arg_num)
array func_get_args ( )
The printf() function we examined previously is able to take an arbitrary number of parameters. That is, it could take just one parameter, or five, or fifty, or five hundred - it can take as many as are passed into it by the user. This is known as a variable-length parameter list, and it is automatically implemented in your user functions. For example:
function some_func($a, $b) {
$j = 1;
}
some_func(1,2,3,4,5,6,7,8);
?>
Here the function some_func() is defined to only take two parameters, $a and $b, but we call it with eight parameters and the script should run without a problem. In that example, 1 will be placed into $a, and 2 will be placed into $b, but what happens to the other parameters?
Coming to your rescue are three functions: func_num_args(), func_get_arg(), and func_get_args(), of which the first and last take no parameters. To get the number of arguments that were passed into your function, call func_num_args() and read its return value. To get the value of an individual parameter, use func_get_arg() and pass in the parameter number you want to retrieve to have its value returned back to you. Finally, func_get_args() returns an array of the parameters that were passed in. Here's an example:
function some_func($a, $b) {
for ($i = 0; $i < func_num_args(); ++$i) {
$param = func_get_arg($i);
echo "Received parameter $param.\n";
}
}
function some_other_func($a, $b) {
$param = func_get_args();
$param = join(", ", $param);
echo "Received parameters: $param.\n";
}
some_func(1,2,3,4,5,6,7,8);
some_other_func(1,2,3,4,5,6,7,8);
?>
Using func_num_args() alone you can easily implement function error checking. You can, for example, start off each of your functions by checking to make sure func_num_args() is what you are expecting, and, if not, exit. Once you add func_get_arg() into the mix, however, you should easily be able to create your own functions that work with any number of parameters.
Functions
Functions, both ones built into PHP and ones you define yourself, make coding much easier - they take away lots of hard work because you can reuse other people's code, and they allow you to keep your scripts shorter and easier to maintain. As PHP 5 includes more than 2,500 functions, you might assume it's a very easy language indeed, but the truth is that each function needs to be used in different ways and so needs to be learnt individually. In this chapter you will learn your first PHP functions, with the most helpful and easy first.
Rather than writing pieces of code time after time whenever you want to execute the same functionality, PHP allows you to encapsulate code into a named function that you can call from elsewhere in your script.
PHP comes with hundreds of predefined functions that perform all manner of tasks from reading files and manipulating strings up to querying databases and connecting to an IRC server. If you find something is missing, you can add your own functions on a script by script basis, and these are called user functions .
In this section we will be covering a variety of the most important basic functions in PHP - more specialised functions can be found spread throughout the book under various sections, and should be looked up using the index.
Topics covered in this chapter are:
*
Working with date and time
*
Mathematical functions
*
String manipulation
*
Creating data hashes
*
Regular expressions
*
Extension handling
*
Writing your own functions
*
Recursive, variable, and callback functions
Rather than writing pieces of code time after time whenever you want to execute the same functionality, PHP allows you to encapsulate code into a named function that you can call from elsewhere in your script.
PHP comes with hundreds of predefined functions that perform all manner of tasks from reading files and manipulating strings up to querying databases and connecting to an IRC server. If you find something is missing, you can add your own functions on a script by script basis, and these are called user functions .
In this section we will be covering a variety of the most important basic functions in PHP - more specialised functions can be found spread throughout the book under various sections, and should be looked up using the index.
Topics covered in this chapter are:
*
Working with date and time
*
Mathematical functions
*
String manipulation
*
Creating data hashes
*
Regular expressions
*
Extension handling
*
Writing your own functions
*
Recursive, variable, and callback functions
Saturday, July 4, 2009
Arrays
An array in PHP is actually an ordered map. A map is a type that maps values to keys. This type is optimized in several ways, so you can use it as a real array, or a list (vector), hashtable (which is an implementation of a map), dictionary, collection, stack, queue and probably more. Because you can have another PHP array as a value, you can also quite easily simulate trees.
Explanation of those data structures is beyond the scope of this manual, but you'll find at least one example for each of them. For more information we refer you to external literature about this broad topic.
Syntax
Specifying with array()
An array can be created by the array() language-construct. It takes a certain number of comma-separated key => value pairs.
array( [key =>] value
, ...
)
// key may be an integer or string
// value may be any value
$arr = array("foo" => "bar", 12 => true);
echo $arr["foo"]; // bar
echo $arr[12]; // 1
?>
A key may be either an integer or a string. If a key is the standard representation of an integer, it will be interpreted as such (i.e. "8" will be interpreted as 8, while "08" will be interpreted as "08"). Floats in key are truncated to integer. There are no different indexed and associative array types in PHP; there is only one array type, which can both contain integer and string indices.
A value can be of any PHP type.
$arr = array("somearray" => array(6 => 5, 13 => 9, "a" => 42));
echo $arr["somearray"][6]; // 5
echo $arr["somearray"][13]; // 9
echo $arr["somearray"]["a"]; // 42
?>
If you do not specify a key for a given value, then the maximum of the integer indices is taken, and the new key will be that maximum value + 1. If you specify a key that already has a value assigned to it, that value will be overwritten.
// This array is the same as ...
array(5 => 43, 32, 56, "b" => 12);
// ...this array
array(5 => 43, 6 => 32, 7 => 56, "b" => 12);
?>
?????
As of PHP 4.3.0, the index generation behaviour described above has changed. Now, if you append to an array in which the current maximum key is negative, then the next key created will be zero (0). Before, the new index would have been set to the largest existing key + 1, the same as positive indices are.
Using TRUE as a key will evaluate to integer 1 as key. Using FALSE as a key will evaluate to integer 0 as key. Using NULL as a key will evaluate to the empty string. Using the empty string as key will create (or overwrite) a key with the empty string and its value; it is not the same as using empty brackets.
You cannot use arrays or objects as keys. Doing so will result in a warning: Illegal offset type.
Creating/modifying with square-bracket syntax
You can also modify an existing array by explicitly setting values in it.
This is done by assigning values to the array while specifying the key in brackets. You can also omit the key, add an empty pair of brackets ("[]") to the variable name in that case. $arr[key] = value;
$arr[] = value;
// key may be an integer or string
// value may be any value
If $arr doesn't exist yet, it will be created. So this is also an alternative way to specify an array. To change a certain value, just assign a new value to an element specified with its key. If you want to remove a key/value pair, you need to unset() it.
$arr = array(5 => 1, 12 => 2);
$arr[] = 56; // This is the same as $arr[13] = 56;
// at this point of the script
$arr["x"] = 42; // This adds a new element to
// the array with key "x"
unset($arr[5]); // This removes the element from the array
unset($arr); // This deletes the whole array
?>
????: As mentioned above, if you provide the brackets with no key specified, then the maximum of the existing integer indices is taken, and the new key will be that maximum value + 1 . If no integer indices exist yet, the key will be 0 (zero). If you specify a key that already has a value assigned to it, that value will be overwritten.
?????
As of PHP 4.3.0, the index generation behaviour described above has changed. Now, if you append to an array in which the current maximum key is negative, then the next key created will be zero (0). Before, the new index would have been set to the largest existing key + 1, the same as positive indices are.
Note that the maximum integer key used for this need not currently exist in the array. It simply must have existed in the array at some time since the last time the array was re-indexed. The following example illustrates:
// Create a simple array.
$array = array(1, 2, 3, 4, 5);
print_r($array);
// Now delete every item, but leave the array itself intact:
foreach ($array as $i => $value) {
unset($array[$i]);
}
print_r($array);
// Append an item (note that the new key is 5, instead of 0 as you
// might expect).
$array[] = 6;
print_r($array);
// Re-index:
$array = array_values($array);
$array[] = 7;
print_r($array);
?>
The above example will output:
Array
(
[0] => 1
[1] => 2
[2] => 3
[3] => 4
[4] => 5
)
Array
(
)
Array
(
[5] => 6
)
Array
(
[0] => 6
[1] => 7
)
Useful functions
There are quite a few useful functions for working with arrays. See the array functions section.
????: The unset() function allows unsetting keys of an array. Be aware that the array will NOT be reindexed. If you only use "usual integer indices" (starting from zero, increasing by one), you can achieve the reindex effect by using array_values().
$a = array(1 => 'one', 2 => 'two', 3 => 'three');
unset($a[2]);
/* will produce an array that would have been defined as
$a = array(1 => 'one', 3 => 'three');
and NOT
$a = array(1 => 'one', 2 =>'three');
*/
$b = array_values($a);
// Now $b is array(0 => 'one', 1 =>'three')
?>
The foreach control structure exists specifically for arrays. It provides an easy way to traverse an array.
Array do's and don'ts
Why is $foo[bar] wrong?
You should always use quotes around a string literal array index. For example, use $foo['bar'] and not $foo[bar]. But why is $foo[bar] wrong? You might have seen the following syntax in old scripts:
$foo[bar] = 'enemy';
echo $foo[bar];
// etc
?>
This is wrong, but it works. Then, why is it wrong? The reason is that this code has an undefined constant (bar) rather than a string ('bar' - notice the quotes), and PHP may in future define constants which, unfortunately for your code, have the same name. It works because PHP automatically converts a bare string (an unquoted string which does not correspond to any known symbol) into a string which contains the bare string. For instance, if there is no defined constant named bar, then PHP will substitute in the string 'bar' and use that.
????: This does not mean to always quote the key. You do not want to quote keys which are constants or variables, as this will prevent PHP from interpreting them.
error_reporting(E_ALL);
ini_set('display_errors', true);
ini_set('html_errors', false);
// Simple array:
$array = array(1, 2);
$count = count($array);
for ($i = 0; $i < $count; $i++) {
echo "\nChecking $i: \n";
echo "Bad: " . $array['$i'] . "\n";
echo "Good: " . $array[$i] . "\n";
echo "Bad: {$array['$i']}\n";
echo "Good: {$array[$i]}\n";
}
?>
????: The above example will output:
Checking 0:
Notice: Undefined index: $i in /path/to/script.html on line 9
Bad:
Good: 1
Notice: Undefined index: $i in /path/to/script.html on line 11
Bad:
Good: 1
Checking 1:
Notice: Undefined index: $i in /path/to/script.html on line 9
Bad:
Good: 2
Notice: Undefined index: $i in /path/to/script.html on line 11
Bad:
Good: 2
More examples to demonstrate this fact:
// Let's show all errors
error_reporting(E_ALL);
$arr = array('fruit' => 'apple', 'veggie' => 'carrot');
// Correct
print $arr['fruit']; // apple
print $arr['veggie']; // carrot
// Incorrect. This works but also throws a PHP error of
// level E_NOTICE because of an undefined constant named fruit
//
// Notice: Use of undefined constant fruit - assumed 'fruit' in...
print $arr[fruit]; // apple
// Let's define a constant to demonstrate what's going on. We
// will assign value 'veggie' to a constant named fruit.
define('fruit', 'veggie');
// Notice the difference now
print $arr['fruit']; // apple
print $arr[fruit]; // carrot
// The following is okay as it's inside a string. Constants are not
// looked for within strings so no E_NOTICE error here
print "Hello $arr[fruit]"; // Hello apple
// With one exception, braces surrounding arrays within strings
// allows constants to be looked for
print "Hello {$arr[fruit]}"; // Hello carrot
print "Hello {$arr['fruit']}"; // Hello apple
// This will not work, results in a parse error such as:
// Parse error: parse error, expecting T_STRING' or T_VARIABLE' or T_NUM_STRING'
// This of course applies to using autoglobals in strings as well
print "Hello $arr['fruit']";
print "Hello $_GET['foo']";
// Concatenation is another option
print "Hello " . $arr['fruit']; // Hello apple
?>
When you turn error_reporting() up to show E_NOTICE level errors (such as setting it to E_ALL) then you will see these errors. By default, error_reporting is turned down to not show them.
As stated in the syntax section, there must be an expression between the square brackets ('[' and ']'). That means that you can write things like this:
echo $arr[somefunc($bar)];
?>
This is an example of using a function return value as the array index. PHP also knows about constants, as you may have seen the E_* ones before.
$error_descriptions[E_ERROR] = "A fatal error has occured";
$error_descriptions[E_WARNING] = "PHP issued a warning";
$error_descriptions[E_NOTICE] = "This is just an informal notice";
?>
Note that E_ERROR is also a valid identifier, just like bar in the first example. But the last example is in fact the same as writing:
$error_descriptions[1] = "A fatal error has occured";
$error_descriptions[2] = "PHP issued a warning";
$error_descriptions[8] = "This is just an informal notice";
?>
because E_ERROR equals 1, etc.
As we already explained in the above examples, $foo[bar] still works but is wrong. It works, because bar is due to its syntax expected to be a constant expression. However, in this case no constant with the name bar exists. PHP now assumes that you meant bar literally, as the string "bar", but that you forgot to write the quotes.
So why is it bad then?
At some point in the future, the PHP team might want to add another constant or keyword, or you may introduce another constant into your application, and then you get in trouble. For example, you already cannot use the words empty and default this way, since they are special reserved keywords.
????: To reiterate, inside a double-quoted string, it's valid to not surround array indexes with quotes so "$foo[bar]" is valid. See the above examples for details on why as well as the section on variable parsing in strings.
Converting to array
For any of the types: integer, float, string, boolean and resource, if you convert a value to an array, you get an array with one element (with index 0), which is the scalar value you started with.
If you convert an object to an array, you get the properties (member variables) of that object as the array's elements. The keys are the member variable names.
If you convert a NULL value to an array, you get an empty array.
Comparing
It is possible to compare arrays by array_diff() and by Array operators.
Examples
The array type in PHP is very versatile, so here will be some examples to show you the full power of arrays.
// this
$a = array( 'color' => 'red',
'taste' => 'sweet',
'shape' => 'round',
'name' => 'apple',
4 // key will be 0
);
// is completely equivalent with
$a['color'] = 'red';
$a['taste'] = 'sweet';
$a['shape'] = 'round';
$a['name'] = 'apple';
$a[] = 4; // key will be 0
$b[] = 'a';
$b[] = 'b';
$b[] = 'c';
// will result in the array array(0 => 'a' , 1 => 'b' , 2 => 'c'),
// or simply array('a', 'b', 'c')
?>
????? 11-6. Using array()
// Array as (property-)map
$map = array( 'version' => 4,
'OS' => 'Linux',
'lang' => 'english',
'short_tags' => true
);
// strictly numerical keys
$array = array( 7,
8,
0,
156,
-10
);
// this is the same as array(0 => 7, 1 => 8, ...)
$switching = array( 10, // key = 0
5 => 6,
3 => 7,
'a' => 4,
11, // key = 6 (maximum of integer-indices was 5)
'8' => 2, // key = 8 (integer!)
'02' => 77, // key = '02'
0 => 12 // the value 10 will be overwritten by 12
);
// empty array
$empty = array();
?>
????? 11-7. Collection
$colors = array('red', 'blue', 'green', 'yellow');
foreach ($colors as $color) {
echo "Do you like $color?\n";
}
?>
The above example will output:
Do you like red?
Do you like blue?
Do you like green?
Do you like yellow?
Changing values of the array directly is possible since PHP 5 by passing them as reference. Prior versions need workaround: ????? 11-8. Collection
// PHP 5
foreach ($colors as &$color) {
$color = strtoupper($color);
}
unset($color); /* ensure that following writes to
$color will not modify the last array element */
// Workaround for older versions
foreach ($colors as $key => $color) {
$colors[$key] = strtoupper($color);
}
print_r($colors);
?>
The above example will output:
Array
(
[0] => RED
[1] => BLUE
[2] => GREEN
[3] => YELLOW
)
This example creates a one-based array. ????? 11-9. One-based index
$firstquarter = array(1 => 'January', 'February', 'March');
print_r($firstquarter);
?>
The above example will output:
Array
(
[1] => 'January'
[2] => 'February'
[3] => 'March'
)
????? 11-10. Filling an array
// fill an array with all items from a directory
$handle = opendir('.');
while (false !== ($file = readdir($handle))) {
$files[] = $file;
}
closedir($handle);
?>
Arrays are ordered. You can also change the order using various sorting functions. See the array functions section for more information. You can count the number of items in an array using the count() function.
????? 11-11. Sorting an array
sort($files);
print_r($files);
?>
Because the value of an array can be anything, it can also be another array. This way you can make recursive and multi-dimensional arrays.
????? 11-12. Recursive and multi-dimensional arrays
$fruits = array ( "fruits" => array ( "a" => "orange",
"b" => "banana",
"c" => "apple"
),
"numbers" => array ( 1,
2,
3,
4,
5,
6
),
"holes" => array ( "first",
5 => "second",
"third"
)
);
// Some examples to address values in the array above
echo $fruits["holes"][5]; // prints "second"
echo $fruits["fruits"]["a"]; // prints "orange"
unset($fruits["holes"][0]); // remove "first"
// Create a new multi-dimensional array
$juices["apple"]["green"] = "good";
?>
You should be aware that array assignment always involves value copying. It also means that the internal array pointer used by current() and similar functions is reset. You need to use the reference operator to copy an array by reference.
$arr1 = array(2, 3);
$arr2 = $arr1;
$arr2[] = 4; // $arr2 is changed,
// $arr1 is still array(2, 3)
$arr3 = &$arr1;
$arr3[] = 4; // now $arr1 and $arr3 are the same
?>
????? ??? ???? ?????
Strings ????? Objects
Explanation of those data structures is beyond the scope of this manual, but you'll find at least one example for each of them. For more information we refer you to external literature about this broad topic.
Syntax
Specifying with array()
An array can be created by the array() language-construct. It takes a certain number of comma-separated key => value pairs.
array( [key =>] value
, ...
)
// key may be an integer or string
// value may be any value
$arr = array("foo" => "bar", 12 => true);
echo $arr["foo"]; // bar
echo $arr[12]; // 1
?>
A key may be either an integer or a string. If a key is the standard representation of an integer, it will be interpreted as such (i.e. "8" will be interpreted as 8, while "08" will be interpreted as "08"). Floats in key are truncated to integer. There are no different indexed and associative array types in PHP; there is only one array type, which can both contain integer and string indices.
A value can be of any PHP type.
$arr = array("somearray" => array(6 => 5, 13 => 9, "a" => 42));
echo $arr["somearray"][6]; // 5
echo $arr["somearray"][13]; // 9
echo $arr["somearray"]["a"]; // 42
?>
If you do not specify a key for a given value, then the maximum of the integer indices is taken, and the new key will be that maximum value + 1. If you specify a key that already has a value assigned to it, that value will be overwritten.
// This array is the same as ...
array(5 => 43, 32, 56, "b" => 12);
// ...this array
array(5 => 43, 6 => 32, 7 => 56, "b" => 12);
?>
?????
As of PHP 4.3.0, the index generation behaviour described above has changed. Now, if you append to an array in which the current maximum key is negative, then the next key created will be zero (0). Before, the new index would have been set to the largest existing key + 1, the same as positive indices are.
Using TRUE as a key will evaluate to integer 1 as key. Using FALSE as a key will evaluate to integer 0 as key. Using NULL as a key will evaluate to the empty string. Using the empty string as key will create (or overwrite) a key with the empty string and its value; it is not the same as using empty brackets.
You cannot use arrays or objects as keys. Doing so will result in a warning: Illegal offset type.
Creating/modifying with square-bracket syntax
You can also modify an existing array by explicitly setting values in it.
This is done by assigning values to the array while specifying the key in brackets. You can also omit the key, add an empty pair of brackets ("[]") to the variable name in that case. $arr[key] = value;
$arr[] = value;
// key may be an integer or string
// value may be any value
If $arr doesn't exist yet, it will be created. So this is also an alternative way to specify an array. To change a certain value, just assign a new value to an element specified with its key. If you want to remove a key/value pair, you need to unset() it.
$arr = array(5 => 1, 12 => 2);
$arr[] = 56; // This is the same as $arr[13] = 56;
// at this point of the script
$arr["x"] = 42; // This adds a new element to
// the array with key "x"
unset($arr[5]); // This removes the element from the array
unset($arr); // This deletes the whole array
?>
????: As mentioned above, if you provide the brackets with no key specified, then the maximum of the existing integer indices is taken, and the new key will be that maximum value + 1 . If no integer indices exist yet, the key will be 0 (zero). If you specify a key that already has a value assigned to it, that value will be overwritten.
?????
As of PHP 4.3.0, the index generation behaviour described above has changed. Now, if you append to an array in which the current maximum key is negative, then the next key created will be zero (0). Before, the new index would have been set to the largest existing key + 1, the same as positive indices are.
Note that the maximum integer key used for this need not currently exist in the array. It simply must have existed in the array at some time since the last time the array was re-indexed. The following example illustrates:
// Create a simple array.
$array = array(1, 2, 3, 4, 5);
print_r($array);
// Now delete every item, but leave the array itself intact:
foreach ($array as $i => $value) {
unset($array[$i]);
}
print_r($array);
// Append an item (note that the new key is 5, instead of 0 as you
// might expect).
$array[] = 6;
print_r($array);
// Re-index:
$array = array_values($array);
$array[] = 7;
print_r($array);
?>
The above example will output:
Array
(
[0] => 1
[1] => 2
[2] => 3
[3] => 4
[4] => 5
)
Array
(
)
Array
(
[5] => 6
)
Array
(
[0] => 6
[1] => 7
)
Useful functions
There are quite a few useful functions for working with arrays. See the array functions section.
????: The unset() function allows unsetting keys of an array. Be aware that the array will NOT be reindexed. If you only use "usual integer indices" (starting from zero, increasing by one), you can achieve the reindex effect by using array_values().
$a = array(1 => 'one', 2 => 'two', 3 => 'three');
unset($a[2]);
/* will produce an array that would have been defined as
$a = array(1 => 'one', 3 => 'three');
and NOT
$a = array(1 => 'one', 2 =>'three');
*/
$b = array_values($a);
// Now $b is array(0 => 'one', 1 =>'three')
?>
The foreach control structure exists specifically for arrays. It provides an easy way to traverse an array.
Array do's and don'ts
Why is $foo[bar] wrong?
You should always use quotes around a string literal array index. For example, use $foo['bar'] and not $foo[bar]. But why is $foo[bar] wrong? You might have seen the following syntax in old scripts:
$foo[bar] = 'enemy';
echo $foo[bar];
// etc
?>
This is wrong, but it works. Then, why is it wrong? The reason is that this code has an undefined constant (bar) rather than a string ('bar' - notice the quotes), and PHP may in future define constants which, unfortunately for your code, have the same name. It works because PHP automatically converts a bare string (an unquoted string which does not correspond to any known symbol) into a string which contains the bare string. For instance, if there is no defined constant named bar, then PHP will substitute in the string 'bar' and use that.
????: This does not mean to always quote the key. You do not want to quote keys which are constants or variables, as this will prevent PHP from interpreting them.
error_reporting(E_ALL);
ini_set('display_errors', true);
ini_set('html_errors', false);
// Simple array:
$array = array(1, 2);
$count = count($array);
for ($i = 0; $i < $count; $i++) {
echo "\nChecking $i: \n";
echo "Bad: " . $array['$i'] . "\n";
echo "Good: " . $array[$i] . "\n";
echo "Bad: {$array['$i']}\n";
echo "Good: {$array[$i]}\n";
}
?>
????: The above example will output:
Checking 0:
Notice: Undefined index: $i in /path/to/script.html on line 9
Bad:
Good: 1
Notice: Undefined index: $i in /path/to/script.html on line 11
Bad:
Good: 1
Checking 1:
Notice: Undefined index: $i in /path/to/script.html on line 9
Bad:
Good: 2
Notice: Undefined index: $i in /path/to/script.html on line 11
Bad:
Good: 2
More examples to demonstrate this fact:
// Let's show all errors
error_reporting(E_ALL);
$arr = array('fruit' => 'apple', 'veggie' => 'carrot');
// Correct
print $arr['fruit']; // apple
print $arr['veggie']; // carrot
// Incorrect. This works but also throws a PHP error of
// level E_NOTICE because of an undefined constant named fruit
//
// Notice: Use of undefined constant fruit - assumed 'fruit' in...
print $arr[fruit]; // apple
// Let's define a constant to demonstrate what's going on. We
// will assign value 'veggie' to a constant named fruit.
define('fruit', 'veggie');
// Notice the difference now
print $arr['fruit']; // apple
print $arr[fruit]; // carrot
// The following is okay as it's inside a string. Constants are not
// looked for within strings so no E_NOTICE error here
print "Hello $arr[fruit]"; // Hello apple
// With one exception, braces surrounding arrays within strings
// allows constants to be looked for
print "Hello {$arr[fruit]}"; // Hello carrot
print "Hello {$arr['fruit']}"; // Hello apple
// This will not work, results in a parse error such as:
// Parse error: parse error, expecting T_STRING' or T_VARIABLE' or T_NUM_STRING'
// This of course applies to using autoglobals in strings as well
print "Hello $arr['fruit']";
print "Hello $_GET['foo']";
// Concatenation is another option
print "Hello " . $arr['fruit']; // Hello apple
?>
When you turn error_reporting() up to show E_NOTICE level errors (such as setting it to E_ALL) then you will see these errors. By default, error_reporting is turned down to not show them.
As stated in the syntax section, there must be an expression between the square brackets ('[' and ']'). That means that you can write things like this:
echo $arr[somefunc($bar)];
?>
This is an example of using a function return value as the array index. PHP also knows about constants, as you may have seen the E_* ones before.
$error_descriptions[E_ERROR] = "A fatal error has occured";
$error_descriptions[E_WARNING] = "PHP issued a warning";
$error_descriptions[E_NOTICE] = "This is just an informal notice";
?>
Note that E_ERROR is also a valid identifier, just like bar in the first example. But the last example is in fact the same as writing:
$error_descriptions[1] = "A fatal error has occured";
$error_descriptions[2] = "PHP issued a warning";
$error_descriptions[8] = "This is just an informal notice";
?>
because E_ERROR equals 1, etc.
As we already explained in the above examples, $foo[bar] still works but is wrong. It works, because bar is due to its syntax expected to be a constant expression. However, in this case no constant with the name bar exists. PHP now assumes that you meant bar literally, as the string "bar", but that you forgot to write the quotes.
So why is it bad then?
At some point in the future, the PHP team might want to add another constant or keyword, or you may introduce another constant into your application, and then you get in trouble. For example, you already cannot use the words empty and default this way, since they are special reserved keywords.
????: To reiterate, inside a double-quoted string, it's valid to not surround array indexes with quotes so "$foo[bar]" is valid. See the above examples for details on why as well as the section on variable parsing in strings.
Converting to array
For any of the types: integer, float, string, boolean and resource, if you convert a value to an array, you get an array with one element (with index 0), which is the scalar value you started with.
If you convert an object to an array, you get the properties (member variables) of that object as the array's elements. The keys are the member variable names.
If you convert a NULL value to an array, you get an empty array.
Comparing
It is possible to compare arrays by array_diff() and by Array operators.
Examples
The array type in PHP is very versatile, so here will be some examples to show you the full power of arrays.
// this
$a = array( 'color' => 'red',
'taste' => 'sweet',
'shape' => 'round',
'name' => 'apple',
4 // key will be 0
);
// is completely equivalent with
$a['color'] = 'red';
$a['taste'] = 'sweet';
$a['shape'] = 'round';
$a['name'] = 'apple';
$a[] = 4; // key will be 0
$b[] = 'a';
$b[] = 'b';
$b[] = 'c';
// will result in the array array(0 => 'a' , 1 => 'b' , 2 => 'c'),
// or simply array('a', 'b', 'c')
?>
????? 11-6. Using array()
// Array as (property-)map
$map = array( 'version' => 4,
'OS' => 'Linux',
'lang' => 'english',
'short_tags' => true
);
// strictly numerical keys
$array = array( 7,
8,
0,
156,
-10
);
// this is the same as array(0 => 7, 1 => 8, ...)
$switching = array( 10, // key = 0
5 => 6,
3 => 7,
'a' => 4,
11, // key = 6 (maximum of integer-indices was 5)
'8' => 2, // key = 8 (integer!)
'02' => 77, // key = '02'
0 => 12 // the value 10 will be overwritten by 12
);
// empty array
$empty = array();
?>
????? 11-7. Collection
$colors = array('red', 'blue', 'green', 'yellow');
foreach ($colors as $color) {
echo "Do you like $color?\n";
}
?>
The above example will output:
Do you like red?
Do you like blue?
Do you like green?
Do you like yellow?
Changing values of the array directly is possible since PHP 5 by passing them as reference. Prior versions need workaround: ????? 11-8. Collection
// PHP 5
foreach ($colors as &$color) {
$color = strtoupper($color);
}
unset($color); /* ensure that following writes to
$color will not modify the last array element */
// Workaround for older versions
foreach ($colors as $key => $color) {
$colors[$key] = strtoupper($color);
}
print_r($colors);
?>
The above example will output:
Array
(
[0] => RED
[1] => BLUE
[2] => GREEN
[3] => YELLOW
)
This example creates a one-based array. ????? 11-9. One-based index
$firstquarter = array(1 => 'January', 'February', 'March');
print_r($firstquarter);
?>
The above example will output:
Array
(
[1] => 'January'
[2] => 'February'
[3] => 'March'
)
????? 11-10. Filling an array
// fill an array with all items from a directory
$handle = opendir('.');
while (false !== ($file = readdir($handle))) {
$files[] = $file;
}
closedir($handle);
?>
Arrays are ordered. You can also change the order using various sorting functions. See the array functions section for more information. You can count the number of items in an array using the count() function.
????? 11-11. Sorting an array
sort($files);
print_r($files);
?>
Because the value of an array can be anything, it can also be another array. This way you can make recursive and multi-dimensional arrays.
????? 11-12. Recursive and multi-dimensional arrays
$fruits = array ( "fruits" => array ( "a" => "orange",
"b" => "banana",
"c" => "apple"
),
"numbers" => array ( 1,
2,
3,
4,
5,
6
),
"holes" => array ( "first",
5 => "second",
"third"
)
);
// Some examples to address values in the array above
echo $fruits["holes"][5]; // prints "second"
echo $fruits["fruits"]["a"]; // prints "orange"
unset($fruits["holes"][0]); // remove "first"
// Create a new multi-dimensional array
$juices["apple"]["green"] = "good";
?>
You should be aware that array assignment always involves value copying. It also means that the internal array pointer used by current() and similar functions is reset. You need to use the reference operator to copy an array by reference.
$arr1 = array(2, 3);
$arr2 = $arr1;
$arr2[] = 4; // $arr2 is changed,
// $arr1 is still array(2, 3)
$arr3 = &$arr1;
$arr3[] = 4; // now $arr1 and $arr3 are the same
?>
????? ??? ???? ?????
Strings ????? Objects
Strings
A string is series of characters. In PHP, a character is the same as a byte, that is, there are exactly 256 different characters possible. This also implies that PHP has no native support of Unicode. See utf8_encode() and utf8_decode() for some Unicode support.
????: It is no problem for a string to become very large. There is no practical bound to the size of strings imposed by PHP, so there is no reason at all to worry about long strings.
Syntax
A string literal can be specified in three different ways.
single quoted
double quoted
heredoc syntax
Single quoted
The easiest way to specify a simple string is to enclose it in single quotes (the character ').
To specify a literal single quote, you will need to escape it with a backslash (\), like in many other languages. If a backslash needs to occur before a single quote or at the end of the string, you need to double it. Note that if you try to escape any other character, the backslash will also be printed! So usually there is no need to escape the backslash itself.
????: In PHP 3, a warning will be issued at the E_NOTICE level when this happens.
????: Unlike the two other syntaxes, variables and escape sequences for special characters will not be expanded when they occur in single quoted strings.
echo 'this is a simple string';
echo 'You can also have embedded newlines in
strings this way as it is
okay to do';
// Outputs: Arnold once said: "I'll be back"
echo 'Arnold once said: "I\'ll be back"';
// Outputs: You deleted C:\*.*?
echo 'You deleted C:\\*.*?';
// Outputs: You deleted C:\*.*?
echo 'You deleted C:\*.*?';
// Outputs: This will not expand: \n a newline
echo 'This will not expand: \n a newline';
// Outputs: Variables do not $expand $either
echo 'Variables do not $expand $either';
?>
Double quoted
If the string is enclosed in double-quotes ("), PHP understands more escape sequences for special characters:
???? 11-1. Escaped characters
sequence meaning
\n linefeed (LF or 0x0A (10) in ASCII)
\r carriage return (CR or 0x0D (13) in ASCII)
\t horizontal tab (HT or 0x09 (9) in ASCII)
\\ backslash
\$ dollar sign
\" double-quote
\[0-7]{1,3} the sequence of characters matching the regular expression is a character in octal notation
\x[0-9A-Fa-f]{1,2} the sequence of characters matching the regular expression is a character in hexadecimal notation
Again, if you try to escape any other character, the backslash will be printed too! Before PHP 5.1.1, backslash in \{$var} hasn't been printed.
But the most important feature of double-quoted strings is the fact that variable names will be expanded. See string parsing for details.
Heredoc
Another way to delimit strings is by using heredoc syntax ("<<<"). One should provide an identifier after <<<, then the string, and then the same identifier to close the quotation.
The closing identifier must begin in the first column of the line. Also, the identifier used must follow the same naming rules as any other label in PHP: it must contain only alphanumeric characters and underscores, and must start with a non-digit character or underscore.
?????
It is very important to note that the line with the closing identifier contains no other characters, except possibly a semicolon (;). That means especially that the identifier may not be indented, and there may not be any spaces or tabs after or before the semicolon. It's also important to realize that the first character before the closing identifier must be a newline as defined by your operating system. This is \r on Macintosh for example. Closing delimiter (possibly followed by a semicolon) must be followed by a newline too.
If this rule is broken and the closing identifier is not "clean" then it's not considered to be a closing identifier and PHP will continue looking for one. If in this case a proper closing identifier is not found then a parse error will result with the line number being at the end of the script.
It is not allowed to use heredoc syntax in initializing class members. Use other string syntaxes instead. ????? 11-3. Invalid example
class foo {
public $bar = <<
EOT;
}
?>
Heredoc text behaves just like a double-quoted string, without the double-quotes. This means that you do not need to escape quotes in your here docs, but you can still use the escape codes listed above. Variables are expanded, but the same care must be taken when expressing complex variables inside a heredoc as with strings. ????? 11-4. Heredoc string quoting example
$str = <<
spanning multiple lines
using heredoc syntax.
EOD;
/* More complex example, with variables. */
class foo
{
var $foo;
var $bar;
function foo()
{
$this->foo = 'Foo';
$this->bar = array('Bar1', 'Bar2', 'Bar3');
}
}
$foo = new foo();
$name = 'MyName';
echo <<
Now, I am printing some {$foo->bar[1]}.
This should print a capital 'A': \x41
EOT;
?>
????: Heredoc support was added in PHP 4.
Variable parsing
When a string is specified in double quotes or with heredoc, variables are parsed within it.
There are two types of syntax: a simple one and a complex one. The simple syntax is the most common and convenient. It provides a way to parse a variable, an array value, or an object property.
The complex syntax was introduced in PHP 4, and can be recognised by the curly braces surrounding the expression.
Simple syntax
If a dollar sign ($) is encountered, the parser will greedily take as many tokens as possible to form a valid variable name. Enclose the variable name in curly braces if you want to explicitly specify the end of the name.
$beer = 'Heineken';
echo "$beer's taste is great"; // works, "'" is an invalid character for varnames
echo "He drank some $beers"; // won't work, 's' is a valid character for varnames
echo "He drank some ${beer}s"; // works
echo "He drank some {$beer}s"; // works
?>
Similarly, you can also have an array index or an object property parsed. With array indices, the closing square bracket (]) marks the end of the index. For object properties the same rules apply as to simple variables, though with object properties there doesn't exist a trick like the one with variables.
// These examples are specific to using arrays inside of strings.
// When outside of a string, always quote your array string keys
// and do not use {braces} when outside of strings either.
// Let's show all errors
error_reporting(E_ALL);
$fruits = array('strawberry' => 'red', 'banana' => 'yellow');
// Works but note that this works differently outside string-quotes
echo "A banana is $fruits[banana].";
// Works
echo "A banana is {$fruits['banana']}.";
// Works but PHP looks for a constant named banana first
// as described below.
echo "A banana is {$fruits[banana]}.";
// Won't work, use braces. This results in a parse error.
echo "A banana is $fruits['banana'].";
// Works
echo "A banana is " . $fruits['banana'] . ".";
// Works
echo "This square is $square->width meters broad.";
// Won't work. For a solution, see the complex syntax.
echo "This square is $square->width00 centimeters broad.";
?>
For anything more complex, you should use the complex syntax.
Complex (curly) syntax
This isn't called complex because the syntax is complex, but because you can include complex expressions this way.
In fact, you can include any value that is in the namespace in strings with this syntax. You simply write the expression the same way as you would outside the string, and then include it in { and }. Since you can't escape '{', this syntax will only be recognised when the $ is immediately following the {. (Use "{\$" to get a literal "{$"). Some examples to make it clear:
// Let's show all errors
error_reporting(E_ALL);
$great = 'fantastic';
// Won't work, outputs: This is { fantastic}
echo "This is { $great}";
// Works, outputs: This is fantastic
echo "This is {$great}";
echo "This is ${great}";
// Works
echo "This square is {$square->width}00 centimeters broad.";
// Works
echo "This works: {$arr[4][3]}";
// This is wrong for the same reason as $foo[bar] is wrong
// outside a string. In other words, it will still work but
// because PHP first looks for a constant named foo, it will
// throw an error of level E_NOTICE (undefined constant).
echo "This is wrong: {$arr[foo][3]}";
// Works. When using multi-dimensional arrays, always use
// braces around arrays when inside of strings
echo "This works: {$arr['foo'][3]}";
// Works.
echo "This works: " . $arr['foo'][3];
echo "You can even write {$obj->values[3]->name}";
echo "This is the value of the var named $name: {${$name}}";
?>
String access and modification by character
Characters within strings may be accessed and modified by specifying the zero-based offset of the desired character after the string using square array-brackets like $str[42] so think of a string as an array of characters.
????: They may also be accessed using braces like $str{42} for the same purpose. However, using square array-brackets is preferred.
????? 11-5. Some string examples
// Get the first character of a string
$str = 'This is a test.';
$first = $str[0];
// Get the third character of a string
$third = $str[2];
// Get the last character of a string.
$str = 'This is still a test.';
$last = $str[strlen($str)-1];
// Modify the last character of a string
$str = 'Look at the sea';
$str[strlen($str)-1] = 'e';
// Alternative method using {}
$third = $str{2};
?>
Useful functions and operators
Strings may be concatenated using the '.' (dot) operator. Note that the '+' (addition) operator will not work for this. Please see String operators for more information.
There are a lot of useful functions for string modification.
See the string functions section for general functions, the regular expression functions for advanced find&replacing (in two tastes: Perl and POSIX extended).
There are also functions for URL-strings, and functions to encrypt/decrypt strings (mcrypt and mhash).
Finally, if you still didn't find what you're looking for, see also the character type functions.
Converting to string
You can convert a value to a string using the (string) cast, or the strval() function. String conversion is automatically done in the scope of an expression for you where a string is needed. This happens when you use the echo() or print() functions, or when you compare a variable value to a string. Reading the manual sections on Types and Type Juggling will make the following clearer. See also settype().
A boolean TRUE value is converted to the string "1", the FALSE value is represented as "" (empty string). This way you can convert back and forth between boolean and string values.
An integer or a floating point number (float) is converted to a string representing the number with its digits (including the exponent part for floating point numbers).
Arrays are always converted to the string "Array", so you cannot dump out the contents of an array with echo() or print() to see what is inside them. To view one element, you'd do something like echo $arr['foo']. See below for tips on dumping/viewing the entire contents.
Objects are always converted to the string "Object". If you would like to print out the member variable values of an object for debugging reasons, read the paragraphs below. If you would like to find out the class name of which an object is an instance of, use get_class(). As of PHP 5, __toString() method is used if applicable.
Resources are always converted to strings with the structure "Resource id #1" where 1 is the unique number of the resource assigned by PHP during runtime. If you would like to get the type of the resource, use get_resource_type().
NULL is always converted to an empty string.
As you can see above, printing out the arrays, objects or resources does not provide you any useful information about the values themselves. Look at the functions print_r() and var_dump() for better ways to print out values for debugging.
You can also convert PHP values to strings to store them permanently. This method is called serialization, and can be done with the function serialize(). You can also serialize PHP values to XML structures, if you have WDDX support in your PHP setup.
String conversion to numbers
When a string is evaluated as a numeric value, the resulting value and type are determined as follows.
The string will evaluate as a float if it contains any of the characters '.', 'e', or 'E'. Otherwise, it will evaluate as an integer.
The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero). Valid numeric data is an optional sign, followed by one or more digits (optionally containing a decimal point), followed by an optional exponent. The exponent is an 'e' or 'E' followed by one or more digits.
$foo = 1 + "10.5"; // $foo is float (11.5)
$foo = 1 + "-1.3e3"; // $foo is float (-1299)
$foo = 1 + "bob-1.3e3"; // $foo is integer (1)
$foo = 1 + "bob3"; // $foo is integer (1)
$foo = 1 + "10 Small Pigs"; // $foo is integer (11)
$foo = 4 + "10.2 Little Piggies"; // $foo is float (14.2)
$foo = "10.0 pigs " + 1; // $foo is float (11)
$foo = "10.0 pigs " + 1.0; // $foo is float (11)
?>
For more information on this conversion, see the Unix manual page for strtod(3).
If you would like to test any of the examples in this section, you can cut and paste the examples and insert the following line to see for yourself what's going on:
echo "\$foo==$foo; type is " . gettype ($foo) . "
\n";
?>
Do not expect to get the code of one character by converting it to integer (as you would do in C for example). Use the functions ord() and chr() to convert between charcodes and characters.
????? ??? ???? ?????
Floating point numbers ????? Arrays
????: It is no problem for a string to become very large. There is no practical bound to the size of strings imposed by PHP, so there is no reason at all to worry about long strings.
Syntax
A string literal can be specified in three different ways.
single quoted
double quoted
heredoc syntax
Single quoted
The easiest way to specify a simple string is to enclose it in single quotes (the character ').
To specify a literal single quote, you will need to escape it with a backslash (\), like in many other languages. If a backslash needs to occur before a single quote or at the end of the string, you need to double it. Note that if you try to escape any other character, the backslash will also be printed! So usually there is no need to escape the backslash itself.
????: In PHP 3, a warning will be issued at the E_NOTICE level when this happens.
????: Unlike the two other syntaxes, variables and escape sequences for special characters will not be expanded when they occur in single quoted strings.
echo 'this is a simple string';
echo 'You can also have embedded newlines in
strings this way as it is
okay to do';
// Outputs: Arnold once said: "I'll be back"
echo 'Arnold once said: "I\'ll be back"';
// Outputs: You deleted C:\*.*?
echo 'You deleted C:\\*.*?';
// Outputs: You deleted C:\*.*?
echo 'You deleted C:\*.*?';
// Outputs: This will not expand: \n a newline
echo 'This will not expand: \n a newline';
// Outputs: Variables do not $expand $either
echo 'Variables do not $expand $either';
?>
Double quoted
If the string is enclosed in double-quotes ("), PHP understands more escape sequences for special characters:
???? 11-1. Escaped characters
sequence meaning
\n linefeed (LF or 0x0A (10) in ASCII)
\r carriage return (CR or 0x0D (13) in ASCII)
\t horizontal tab (HT or 0x09 (9) in ASCII)
\\ backslash
\$ dollar sign
\" double-quote
\[0-7]{1,3} the sequence of characters matching the regular expression is a character in octal notation
\x[0-9A-Fa-f]{1,2} the sequence of characters matching the regular expression is a character in hexadecimal notation
Again, if you try to escape any other character, the backslash will be printed too! Before PHP 5.1.1, backslash in \{$var} hasn't been printed.
But the most important feature of double-quoted strings is the fact that variable names will be expanded. See string parsing for details.
Heredoc
Another way to delimit strings is by using heredoc syntax ("<<<"). One should provide an identifier after <<<, then the string, and then the same identifier to close the quotation.
The closing identifier must begin in the first column of the line. Also, the identifier used must follow the same naming rules as any other label in PHP: it must contain only alphanumeric characters and underscores, and must start with a non-digit character or underscore.
?????
It is very important to note that the line with the closing identifier contains no other characters, except possibly a semicolon (;). That means especially that the identifier may not be indented, and there may not be any spaces or tabs after or before the semicolon. It's also important to realize that the first character before the closing identifier must be a newline as defined by your operating system. This is \r on Macintosh for example. Closing delimiter (possibly followed by a semicolon) must be followed by a newline too.
If this rule is broken and the closing identifier is not "clean" then it's not considered to be a closing identifier and PHP will continue looking for one. If in this case a proper closing identifier is not found then a parse error will result with the line number being at the end of the script.
It is not allowed to use heredoc syntax in initializing class members. Use other string syntaxes instead. ????? 11-3. Invalid example
class foo {
public $bar = <<
EOT;
}
?>
Heredoc text behaves just like a double-quoted string, without the double-quotes. This means that you do not need to escape quotes in your here docs, but you can still use the escape codes listed above. Variables are expanded, but the same care must be taken when expressing complex variables inside a heredoc as with strings. ????? 11-4. Heredoc string quoting example
$str = <<
spanning multiple lines
using heredoc syntax.
EOD;
/* More complex example, with variables. */
class foo
{
var $foo;
var $bar;
function foo()
{
$this->foo = 'Foo';
$this->bar = array('Bar1', 'Bar2', 'Bar3');
}
}
$foo = new foo();
$name = 'MyName';
echo <<
Now, I am printing some {$foo->bar[1]}.
This should print a capital 'A': \x41
EOT;
?>
????: Heredoc support was added in PHP 4.
Variable parsing
When a string is specified in double quotes or with heredoc, variables are parsed within it.
There are two types of syntax: a simple one and a complex one. The simple syntax is the most common and convenient. It provides a way to parse a variable, an array value, or an object property.
The complex syntax was introduced in PHP 4, and can be recognised by the curly braces surrounding the expression.
Simple syntax
If a dollar sign ($) is encountered, the parser will greedily take as many tokens as possible to form a valid variable name. Enclose the variable name in curly braces if you want to explicitly specify the end of the name.
$beer = 'Heineken';
echo "$beer's taste is great"; // works, "'" is an invalid character for varnames
echo "He drank some $beers"; // won't work, 's' is a valid character for varnames
echo "He drank some ${beer}s"; // works
echo "He drank some {$beer}s"; // works
?>
Similarly, you can also have an array index or an object property parsed. With array indices, the closing square bracket (]) marks the end of the index. For object properties the same rules apply as to simple variables, though with object properties there doesn't exist a trick like the one with variables.
// These examples are specific to using arrays inside of strings.
// When outside of a string, always quote your array string keys
// and do not use {braces} when outside of strings either.
// Let's show all errors
error_reporting(E_ALL);
$fruits = array('strawberry' => 'red', 'banana' => 'yellow');
// Works but note that this works differently outside string-quotes
echo "A banana is $fruits[banana].";
// Works
echo "A banana is {$fruits['banana']}.";
// Works but PHP looks for a constant named banana first
// as described below.
echo "A banana is {$fruits[banana]}.";
// Won't work, use braces. This results in a parse error.
echo "A banana is $fruits['banana'].";
// Works
echo "A banana is " . $fruits['banana'] . ".";
// Works
echo "This square is $square->width meters broad.";
// Won't work. For a solution, see the complex syntax.
echo "This square is $square->width00 centimeters broad.";
?>
For anything more complex, you should use the complex syntax.
Complex (curly) syntax
This isn't called complex because the syntax is complex, but because you can include complex expressions this way.
In fact, you can include any value that is in the namespace in strings with this syntax. You simply write the expression the same way as you would outside the string, and then include it in { and }. Since you can't escape '{', this syntax will only be recognised when the $ is immediately following the {. (Use "{\$" to get a literal "{$"). Some examples to make it clear:
// Let's show all errors
error_reporting(E_ALL);
$great = 'fantastic';
// Won't work, outputs: This is { fantastic}
echo "This is { $great}";
// Works, outputs: This is fantastic
echo "This is {$great}";
echo "This is ${great}";
// Works
echo "This square is {$square->width}00 centimeters broad.";
// Works
echo "This works: {$arr[4][3]}";
// This is wrong for the same reason as $foo[bar] is wrong
// outside a string. In other words, it will still work but
// because PHP first looks for a constant named foo, it will
// throw an error of level E_NOTICE (undefined constant).
echo "This is wrong: {$arr[foo][3]}";
// Works. When using multi-dimensional arrays, always use
// braces around arrays when inside of strings
echo "This works: {$arr['foo'][3]}";
// Works.
echo "This works: " . $arr['foo'][3];
echo "You can even write {$obj->values[3]->name}";
echo "This is the value of the var named $name: {${$name}}";
?>
String access and modification by character
Characters within strings may be accessed and modified by specifying the zero-based offset of the desired character after the string using square array-brackets like $str[42] so think of a string as an array of characters.
????: They may also be accessed using braces like $str{42} for the same purpose. However, using square array-brackets is preferred.
????? 11-5. Some string examples
// Get the first character of a string
$str = 'This is a test.';
$first = $str[0];
// Get the third character of a string
$third = $str[2];
// Get the last character of a string.
$str = 'This is still a test.';
$last = $str[strlen($str)-1];
// Modify the last character of a string
$str = 'Look at the sea';
$str[strlen($str)-1] = 'e';
// Alternative method using {}
$third = $str{2};
?>
Useful functions and operators
Strings may be concatenated using the '.' (dot) operator. Note that the '+' (addition) operator will not work for this. Please see String operators for more information.
There are a lot of useful functions for string modification.
See the string functions section for general functions, the regular expression functions for advanced find&replacing (in two tastes: Perl and POSIX extended).
There are also functions for URL-strings, and functions to encrypt/decrypt strings (mcrypt and mhash).
Finally, if you still didn't find what you're looking for, see also the character type functions.
Converting to string
You can convert a value to a string using the (string) cast, or the strval() function. String conversion is automatically done in the scope of an expression for you where a string is needed. This happens when you use the echo() or print() functions, or when you compare a variable value to a string. Reading the manual sections on Types and Type Juggling will make the following clearer. See also settype().
A boolean TRUE value is converted to the string "1", the FALSE value is represented as "" (empty string). This way you can convert back and forth between boolean and string values.
An integer or a floating point number (float) is converted to a string representing the number with its digits (including the exponent part for floating point numbers).
Arrays are always converted to the string "Array", so you cannot dump out the contents of an array with echo() or print() to see what is inside them. To view one element, you'd do something like echo $arr['foo']. See below for tips on dumping/viewing the entire contents.
Objects are always converted to the string "Object". If you would like to print out the member variable values of an object for debugging reasons, read the paragraphs below. If you would like to find out the class name of which an object is an instance of, use get_class(). As of PHP 5, __toString() method is used if applicable.
Resources are always converted to strings with the structure "Resource id #1" where 1 is the unique number of the resource assigned by PHP during runtime. If you would like to get the type of the resource, use get_resource_type().
NULL is always converted to an empty string.
As you can see above, printing out the arrays, objects or resources does not provide you any useful information about the values themselves. Look at the functions print_r() and var_dump() for better ways to print out values for debugging.
You can also convert PHP values to strings to store them permanently. This method is called serialization, and can be done with the function serialize(). You can also serialize PHP values to XML structures, if you have WDDX support in your PHP setup.
String conversion to numbers
When a string is evaluated as a numeric value, the resulting value and type are determined as follows.
The string will evaluate as a float if it contains any of the characters '.', 'e', or 'E'. Otherwise, it will evaluate as an integer.
The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero). Valid numeric data is an optional sign, followed by one or more digits (optionally containing a decimal point), followed by an optional exponent. The exponent is an 'e' or 'E' followed by one or more digits.
$foo = 1 + "10.5"; // $foo is float (11.5)
$foo = 1 + "-1.3e3"; // $foo is float (-1299)
$foo = 1 + "bob-1.3e3"; // $foo is integer (1)
$foo = 1 + "bob3"; // $foo is integer (1)
$foo = 1 + "10 Small Pigs"; // $foo is integer (11)
$foo = 4 + "10.2 Little Piggies"; // $foo is float (14.2)
$foo = "10.0 pigs " + 1; // $foo is float (11)
$foo = "10.0 pigs " + 1.0; // $foo is float (11)
?>
For more information on this conversion, see the Unix manual page for strtod(3).
If you would like to test any of the examples in this section, you can cut and paste the examples and insert the following line to see for yourself what's going on:
echo "\$foo==$foo; type is " . gettype ($foo) . "
\n";
?>
Do not expect to get the code of one character by converting it to integer (as you would do in C for example). Use the functions ord() and chr() to convert between charcodes and characters.
????? ??? ???? ?????
Floating point numbers ????? Arrays
Floating point numbers
Floating point numbers (AKA "floats", "doubles" or "real numbers") can be specified using any of the following syntaxes:
$a = 1.234;
$b = 1.2e3;
$c = 7E-10;
?>
Formally:
LNUM [0-9]+
DNUM ([0-9]*[\.]{LNUM}) | ({LNUM}[\.][0-9]*)
EXPONENT_DNUM ( ({LNUM} | {DNUM}) [eE][+-]? {LNUM})
The size of a float is platform-dependent, although a maximum of ~1.8e308 with a precision of roughly 14 decimal digits is a common value (that's 64 bit IEEE format).
Floating point precision
It is quite usual that simple decimal fractions like 0.1 or 0.7 cannot be converted into their internal binary counterparts without a little loss of precision. This can lead to confusing results: for example, floor((0.1+0.7)*10) will usually return 7 instead of the expected 8 as the result of the internal representation really being something like 7.9999999999....
This is related to the fact that it is impossible to exactly express some fractions in decimal notation with a finite number of digits. For instance, 1/3 in decimal form becomes 0.3333333. . ..
So never trust floating number results to the last digit and never compare floating point numbers for equality. If you really need higher precision, you should use the arbitrary precision math functions or gmp functions instead.
Converting to float
For information on when and how strings are converted to floats, see the section titled String conversion to numbers. For values of other types, the conversion is the same as if the value would have been converted to integer and then to float. See the Converting to integer section for more information. As of PHP 5, notice is thrown if you try to convert object to float.
$a = 1.234;
$b = 1.2e3;
$c = 7E-10;
?>
Formally:
LNUM [0-9]+
DNUM ([0-9]*[\.]{LNUM}) | ({LNUM}[\.][0-9]*)
EXPONENT_DNUM ( ({LNUM} | {DNUM}) [eE][+-]? {LNUM})
The size of a float is platform-dependent, although a maximum of ~1.8e308 with a precision of roughly 14 decimal digits is a common value (that's 64 bit IEEE format).
Floating point precision
It is quite usual that simple decimal fractions like 0.1 or 0.7 cannot be converted into their internal binary counterparts without a little loss of precision. This can lead to confusing results: for example, floor((0.1+0.7)*10) will usually return 7 instead of the expected 8 as the result of the internal representation really being something like 7.9999999999....
This is related to the fact that it is impossible to exactly express some fractions in decimal notation with a finite number of digits. For instance, 1/3 in decimal form becomes 0.3333333. . ..
So never trust floating number results to the last digit and never compare floating point numbers for equality. If you really need higher precision, you should use the arbitrary precision math functions or gmp functions instead.
Converting to float
For information on when and how strings are converted to floats, see the section titled String conversion to numbers. For values of other types, the conversion is the same as if the value would have been converted to integer and then to float. See the Converting to integer section for more information. As of PHP 5, notice is thrown if you try to convert object to float.
Integers
Integers
An integer is a number of the set Z = {..., -2, -1, 0, 1, 2, ...}.
See also: Arbitrary length integer / GMP, Floating point numbers, and Arbitrary precision / BCMath
Syntax
Integers can be specified in decimal (10-based), hexadecimal (16-based) or octal (8-based) notation, optionally preceded by a sign (- or +).
If you use the octal notation, you must precede the number with a 0 (zero), to use hexadecimal notation precede the number with 0x. ????? 11-1. Integer literals
$a = 1234; // decimal number
$a = -123; // a negative number
$a = 0123; // octal number (equivalent to 83 decimal)
$a = 0x1A; // hexadecimal number (equivalent to 26 decimal)
?>
Formally the possible structure for integer literals is:
decimal : [1-9][0-9]*
| 0
hexadecimal : 0[xX][0-9a-fA-F]+
octal : 0[0-7]+
integer : [+-]?decimal
| [+-]?hexadecimal
| [+-]?octal
The size of an integer is platform-dependent, although a maximum value of about two billion is the usual value (that's 32 bits signed). PHP does not support unsigned integers.
?????
If an invalid digit is passed to octal integer (i.e. 8 or 9), the rest of the number is ignored. ????? 11-2. Octal weirdness
var_dump(01090); // 010 octal = 8 decimal
?>
Integer overflow
If you specify a number beyond the bounds of the integer type, it will be interpreted as a float instead. Also, if you perform an operation that results in a number beyond the bounds of the integer type, a float will be returned instead.
$large_number = 2147483647;
var_dump($large_number);
// output: int(2147483647)
$large_number = 2147483648;
var_dump($large_number);
// output: float(2147483648)
// it's true also for hexadecimal specified integers between 2^31 and 2^32-1:
var_dump( 0xffffffff );
// output: float(4294967295)
// this doesn't go for hexadecimal specified integers above 2^32-1:
var_dump( 0x100000000 );
// output: int(2147483647)
$million = 1000000;
$large_number = 50000 * $million;
var_dump($large_number);
// output: float(50000000000)
?>
?????
Unfortunately, there was a bug in PHP so that this does not always work correctly when there are negative numbers involved. For example: when you do -50000 * $million, the result will be -429496728. However, when both operands are positive there is no problem.
This is solved in PHP 4.1.0.
There is no integer division operator in PHP. 1/2 yields the float 0.5. You can cast the value to an integer to always round it downwards, or you can use the round() function.
var_dump(25/7); // float(3.5714285714286)
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7)); // float(4)
?>
Converting to integer
To explicitly convert a value to integer, use either the (int) or the (integer) cast. However, in most cases you do not need to use the cast, since a value will be automatically converted if an operator, function or control structure requires an integer argument. You can also convert a value to integer with the function intval().
See also type-juggling.
From booleans
FALSE will yield 0 (zero), and TRUE will yield 1 (one).
From floating point numbers
When converting from float to integer, the number will be rounded towards zero.
If the float is beyond the boundaries of integer (usually +/- 2.15e+9 = 2^31), the result is undefined, since the float hasn't got enough precision to give an exact integer result. No warning, not even a notice will be issued in this case!
?????
Never cast an unknown fraction to integer, as this can sometimes lead to unexpected results.
echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
?>
See for more information the warning about float-precision.
An integer is a number of the set Z = {..., -2, -1, 0, 1, 2, ...}.
See also: Arbitrary length integer / GMP, Floating point numbers, and Arbitrary precision / BCMath
Syntax
Integers can be specified in decimal (10-based), hexadecimal (16-based) or octal (8-based) notation, optionally preceded by a sign (- or +).
If you use the octal notation, you must precede the number with a 0 (zero), to use hexadecimal notation precede the number with 0x. ????? 11-1. Integer literals
$a = 1234; // decimal number
$a = -123; // a negative number
$a = 0123; // octal number (equivalent to 83 decimal)
$a = 0x1A; // hexadecimal number (equivalent to 26 decimal)
?>
Formally the possible structure for integer literals is:
decimal : [1-9][0-9]*
| 0
hexadecimal : 0[xX][0-9a-fA-F]+
octal : 0[0-7]+
integer : [+-]?decimal
| [+-]?hexadecimal
| [+-]?octal
The size of an integer is platform-dependent, although a maximum value of about two billion is the usual value (that's 32 bits signed). PHP does not support unsigned integers.
?????
If an invalid digit is passed to octal integer (i.e. 8 or 9), the rest of the number is ignored. ????? 11-2. Octal weirdness
var_dump(01090); // 010 octal = 8 decimal
?>
Integer overflow
If you specify a number beyond the bounds of the integer type, it will be interpreted as a float instead. Also, if you perform an operation that results in a number beyond the bounds of the integer type, a float will be returned instead.
$large_number = 2147483647;
var_dump($large_number);
// output: int(2147483647)
$large_number = 2147483648;
var_dump($large_number);
// output: float(2147483648)
// it's true also for hexadecimal specified integers between 2^31 and 2^32-1:
var_dump( 0xffffffff );
// output: float(4294967295)
// this doesn't go for hexadecimal specified integers above 2^32-1:
var_dump( 0x100000000 );
// output: int(2147483647)
$million = 1000000;
$large_number = 50000 * $million;
var_dump($large_number);
// output: float(50000000000)
?>
?????
Unfortunately, there was a bug in PHP so that this does not always work correctly when there are negative numbers involved. For example: when you do -50000 * $million, the result will be -429496728. However, when both operands are positive there is no problem.
This is solved in PHP 4.1.0.
There is no integer division operator in PHP. 1/2 yields the float 0.5. You can cast the value to an integer to always round it downwards, or you can use the round() function.
var_dump(25/7); // float(3.5714285714286)
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7)); // float(4)
?>
Converting to integer
To explicitly convert a value to integer, use either the (int) or the (integer) cast. However, in most cases you do not need to use the cast, since a value will be automatically converted if an operator, function or control structure requires an integer argument. You can also convert a value to integer with the function intval().
See also type-juggling.
From booleans
FALSE will yield 0 (zero), and TRUE will yield 1 (one).
From floating point numbers
When converting from float to integer, the number will be rounded towards zero.
If the float is beyond the boundaries of integer (usually +/- 2.15e+9 = 2^31), the result is undefined, since the float hasn't got enough precision to give an exact integer result. No warning, not even a notice will be issued in this case!
?????
Never cast an unknown fraction to integer, as this can sometimes lead to unexpected results.
echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
?>
See for more information the warning about float-precision.
Booleans
This is the easiest type. A boolean expresses a truth value. It can be either TRUE or FALSE.
????: The boolean type was introduced in PHP 4.
Syntax
To specify a boolean literal, use either the keyword TRUE or FALSE. Both are case-insensitive.
$foo = True; // assign the value TRUE to $foo
?>
Usually you use some kind of operator which returns a boolean value, and then pass it on to a control structure.
// == is an operator which test
// equality and returns a boolean
if ($action == "show_version") {
echo "The version is 1.23";
}
// this is not necessary...
if ($show_separators == TRUE) {
echo "
\n";
}
// ...because you can simply type
if ($show_separators) {
echo "
\n";
}
?>
Converting to boolean
To explicitly convert a value to boolean, use either the (bool) or the (boolean) cast. However, in most cases you do not need to use the cast, since a value will be automatically converted if an operator, function or control structure requires a boolean argument.
See also Type Juggling.
When converting to boolean, the following values are considered FALSE:
the boolean FALSE itself
the integer 0 (zero)
the float 0.0 (zero)
the empty string, and the string "0"
an array with zero elements
an object with zero member variables (PHP 4 only)
the special type NULL (including unset variables)
SimpleXML objects created from empty tags
Every other value is considered TRUE (including any resource).
?????
-1 is considered TRUE, like any other non-zero (whether negative or positive) number!
var_dump((bool) ""); // bool(false)
var_dump((bool) 1); // bool(true)
var_dump((bool) -2); // bool(true)
var_dump((bool) "foo"); // bool(true)
var_dump((bool) 2.3e5); // bool(true)
var_dump((bool) array(12)); // bool(true)
var_dump((bool) array()); // bool(false)
var_dump((bool) "false"); // bool(true)
?>
????: The boolean type was introduced in PHP 4.
Syntax
To specify a boolean literal, use either the keyword TRUE or FALSE. Both are case-insensitive.
$foo = True; // assign the value TRUE to $foo
?>
Usually you use some kind of operator which returns a boolean value, and then pass it on to a control structure.
// == is an operator which test
// equality and returns a boolean
if ($action == "show_version") {
echo "The version is 1.23";
}
// this is not necessary...
if ($show_separators == TRUE) {
echo "
\n";
}
// ...because you can simply type
if ($show_separators) {
echo "
\n";
}
?>
Converting to boolean
To explicitly convert a value to boolean, use either the (bool) or the (boolean) cast. However, in most cases you do not need to use the cast, since a value will be automatically converted if an operator, function or control structure requires a boolean argument.
See also Type Juggling.
When converting to boolean, the following values are considered FALSE:
the boolean FALSE itself
the integer 0 (zero)
the float 0.0 (zero)
the empty string, and the string "0"
an array with zero elements
an object with zero member variables (PHP 4 only)
the special type NULL (including unset variables)
SimpleXML objects created from empty tags
Every other value is considered TRUE (including any resource).
?????
-1 is considered TRUE, like any other non-zero (whether negative or positive) number!
var_dump((bool) ""); // bool(false)
var_dump((bool) 1); // bool(true)
var_dump((bool) -2); // bool(true)
var_dump((bool) "foo"); // bool(true)
var_dump((bool) 2.3e5); // bool(true)
var_dump((bool) array(12)); // bool(true)
var_dump((bool) array()); // bool(false)
var_dump((bool) "false"); // bool(true)
?>
PHP supports eight primitive types.
Four scalar types:
boolean
integer
float (floating-point number, aka 'double')
string
Two compound types:
array
object
And finally two special types:
resource
NULL
This manual also introduces some pseudo-types for readability reasons:
mixed
number
callback
You may also find some references to the type "double". Consider double the same as float, the two names exist only for historic reasons.
The type of a variable is usually not set by the programmer; rather, it is decided at runtime by PHP depending on the context in which that variable is used.
????: If you want to check out the type and value of a certain expression, use var_dump().
????: If you simply want a human-readable representation of the type for debugging, use gettype(). To check for a certain type, do not use gettype(), but use the is_type functions. Some examples:
$a_bool = TRUE; // a boolean
$a_str = "foo"; // a string
$a_str2 = 'foo'; // a string
$an_int = 12; // an integer
echo gettype($a_bool); // prints out: boolean
echo gettype($a_str); // prints out: string
// If this is an integer, increment it by four
if (is_int($an_int)) {
$an_int += 4;
}
// If $bool is a string, print it out
// (does not print out anything)
if (is_string($a_bool)) {
echo "String: $a_bool";
}
?>
If you would like to force a variable to be converted to a certain type, you may either cast the variable or use the settype() function on it.
Note that a variable may be evaluated with different values in certain situations, depending on what type it is at the time. For more information, see the section on Type Juggling. Also, you may be interested in viewing the type comparison tables, as they show examples of various type related comparisons.
boolean
integer
float (floating-point number, aka 'double')
string
Two compound types:
array
object
And finally two special types:
resource
NULL
This manual also introduces some pseudo-types for readability reasons:
mixed
number
callback
You may also find some references to the type "double". Consider double the same as float, the two names exist only for historic reasons.
The type of a variable is usually not set by the programmer; rather, it is decided at runtime by PHP depending on the context in which that variable is used.
????: If you want to check out the type and value of a certain expression, use var_dump().
????: If you simply want a human-readable representation of the type for debugging, use gettype(). To check for a certain type, do not use gettype(), but use the is_type functions. Some examples:
$a_bool = TRUE; // a boolean
$a_str = "foo"; // a string
$a_str2 = 'foo'; // a string
$an_int = 12; // an integer
echo gettype($a_bool); // prints out: boolean
echo gettype($a_str); // prints out: string
// If this is an integer, increment it by four
if (is_int($an_int)) {
$an_int += 4;
}
// If $bool is a string, print it out
// (does not print out anything)
if (is_string($a_bool)) {
echo "String: $a_bool";
}
?>
If you would like to force a variable to be converted to a certain type, you may either cast the variable or use the settype() function on it.
Note that a variable may be evaluated with different values in certain situations, depending on what type it is at the time. For more information, see the section on Type Juggling. Also, you may be interested in viewing the type comparison tables, as they show examples of various type related comparisons.
Escaping from HTML
When PHP parses a file, it looks for opening and closing tags, which tell PHP to start and stop interpreting the code between them. Parsing in this manner allows php to be embedded in all sorts of different documents, as everything outside of a pair of opening and closing tags is ignored by the PHP parser. Most of the time you will see php embedded in HTML documents, as in this example.
You can also use more advanced structures: ????? 10-1. Advanced escaping
if ($expression) {
?>
This is true.
} else {
?>
This is false.
}
?>
This works as expected, because when PHP hits the ?> closing tags, it simply starts outputting whatever it finds until it hits another opening tag. The example given here is contrived, of course, but for outputting large blocks of text, dropping out of PHP parsing mode is generally more efficient than sending all of the text through echo() or print().
There are four different pairs of opening and closing tags which can be used in php. Two of those, and , are always available. The other two are short tags and ASP style tags, and can be turned on and off from the php.ini configuration file. As such, while some people find short tags and ASP style tags convenient, they are less portable, and generally not recommended.
????: Also note that if you are embedding PHP within XML or XHTML you will need to use the tags to remain compliant with standards.
????? 10-2. PHP Opening and Closing Tags
1.
2.
3.
This is a shortcut for ""
4. <% echo 'You may optionally use ASP-style tags'; %>
<%= $variable; # This is a shortcut for "<% echo . . ." %>
While the tags seen in examples one and two are both always available, example one is the most commonly used, and recommended, of the two.
Short tags (example three) are only available when they are enabled via the short_open_tag php.ini configuration file directive, or if php was configured with the --enable-short-tags option.
????: If you are using PHP 3 you may also enable short tags via the short_tags() function. This is only available in PHP 3!
ASP style tags (example four) are only available when they are enabled via the asp_tags php.ini configuration file directive.
????: Support for ASP tags was added in 3.0.4.
????: Using short tags should be avoided when developing applications or libraries that are meant for redistribution, or deployment on PHP servers which are not under your control, because short tags may not be supported on the target server. For portable, redistributable code, be sure not to use short tags.
This is going to be ignored.
This will also be ignored.
You can also use more advanced structures: ????? 10-1. Advanced escaping
if ($expression) {
?>
This is true.
} else {
?>
This is false.
}
?>
This works as expected, because when PHP hits the ?> closing tags, it simply starts outputting whatever it finds until it hits another opening tag. The example given here is contrived, of course, but for outputting large blocks of text, dropping out of PHP parsing mode is generally more efficient than sending all of the text through echo() or print().
There are four different pairs of opening and closing tags which can be used in php. Two of those, and , are always available. The other two are short tags and ASP style tags, and can be turned on and off from the php.ini configuration file. As such, while some people find short tags and ASP style tags convenient, they are less portable, and generally not recommended.
????: Also note that if you are embedding PHP within XML or XHTML you will need to use the tags to remain compliant with standards.
????? 10-2. PHP Opening and Closing Tags
1.
2.
3.
This is a shortcut for ""
4. <% echo 'You may optionally use ASP-style tags'; %>
<%= $variable; # This is a shortcut for "<% echo . . ." %>
While the tags seen in examples one and two are both always available, example one is the most commonly used, and recommended, of the two.
Short tags (example three) are only available when they are enabled via the short_open_tag php.ini configuration file directive, or if php was configured with the --enable-short-tags option.
????: If you are using PHP 3 you may also enable short tags via the short_tags() function. This is only available in PHP 3!
ASP style tags (example four) are only available when they are enabled via the asp_tags php.ini configuration file directive.
????: Support for ASP tags was added in 3.0.4.
????: Using short tags should be avoided when developing applications or libraries that are meant for redistribution, or deployment on PHP servers which are not under your control, because short tags may not be supported on the target server. For portable, redistributable code, be sure not to use short tags.
Dealing with Forms
One of the most powerful features of PHP is the way it handles HTML forms. The basic concept that is important to understand is that any form element will automatically be available to your PHP scripts. Please read the manual section on Variables from outside of PHP for more information and examples on using forms with PHP. Here is an example HTML form:
????? 2-6. A simple HTML form
There is nothing special about this form. It is a straight HTML form with no special tags of any kind. When the user fills in this form and hits the submit button, the action.php page is called. In this file you would write something like this:
????? 2-7. Printing data from our form
Hi .
You are years old.
A sample output of this script may be:
Hi Joe. You are 22 years old.
It should be obvious what this does. There is nothing more to it. The $_POST['name'] and $_POST['age'] variables are automatically set for you by PHP. Earlier we used the $_SERVER autoglobal; above we just introduced the $_POST autoglobal which contains all POST data. Notice how the method of our form is POST. If we used the method GET then our form information would live in the $_GET autoglobal instead. You may also use the $_REQUEST autoglobal, if you do not care about the source of your request data. It contains the merged information of GET, POST and COOKIE data. Also see the import_request_variables() function.
You can also deal with XForms input in PHP, although you will find yourself comfortable with the well supported HTML forms for quite some time. While working with XForms is not for beginners, you might be interested in them. We also have a short introduction to handling data received from XForms in our features section.
????? 2-6. A simple HTML form
There is nothing special about this form. It is a straight HTML form with no special tags of any kind. When the user fills in this form and hits the submit button, the action.php page is called. In this file you would write something like this:
????? 2-7. Printing data from our form
Hi .
You are years old.
A sample output of this script may be:
Hi Joe. You are 22 years old.
It should be obvious what this does. There is nothing more to it. The $_POST['name'] and $_POST['age'] variables are automatically set for you by PHP. Earlier we used the $_SERVER autoglobal; above we just introduced the $_POST autoglobal which contains all POST data. Notice how the method of our form is POST. If we used the method GET then our form information would live in the $_GET autoglobal instead. You may also use the $_REQUEST autoglobal, if you do not care about the source of your request data. It contains the merged information of GET, POST and COOKIE data. Also see the import_request_variables() function.
You can also deal with XForms input in PHP, although you will find yourself comfortable with the well supported HTML forms for quite some time. While working with XForms is not for beginners, you might be interested in them. We also have a short introduction to handling data received from XForms in our features section.
Something Useful
Something Useful
Let us do something more useful now. We are going to check what sort of browser the visitor is using. For that, we check the user agent string the browser sends as part of the HTTP request. This information is stored in a variable. Variables always start with a dollar-sign in PHP. The variable we are interested in right now is $_SERVER['HTTP_USER_AGENT'].
????: $_SERVER is a special reserved PHP variable that contains all web server information. It is known as an autoglobal (or superglobal). See the related manual page on superglobals for more information. These special variables were introduced in PHP 4.1.0. Before this time, we used the older $HTTP_*_VARS arrays instead, such as $HTTP_SERVER_VARS. Although deprecated, these older variables still exist. (See also the note on old code.)
To display this variable, you can simply do:
????? 2-3. Printing a variable (Array element)
A sample output of this script may be:
Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
There are many types of variables available in PHP. In the above example we printed an Array element. Arrays can be very useful.
$_SERVER is just one variable that PHP automatically makes available to you. A list can be seen in the Reserved Variables section of the manual or you can get a complete list of them by looking at the output of the phpinfo() function used in the example in the previous section.
You can put multiple PHP statements inside a PHP tag and create little blocks of code that do more than just a single echo. For example, if you want to check for Internet Explorer you can do this:
????? 2-4. Example using control structures and functions
if (strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== FALSE) {
echo 'You are using Internet Explorer.
';
}
?>
A sample output of this script may be:
You are using Internet Explorer.
Here we introduce a couple of new concepts. We have an if statement. If you are familiar with the basic syntax used by the C language, this should look logical to you. Otherwise, you should probably pick up an introductory PHP book and read the first couple of chapters, or read the Language Reference part of the manual. You can find a list of PHP books at http://www.php.net/books.php.
The second concept we introduced was the strpos() function call. strpos() is a function built into PHP which searches a string for another string. In this case we are looking for 'MSIE' (so-called needle) inside $_SERVER['HTTP_USER_AGENT'] (so-called haystack). If the needle is found inside the haystack, the function returns the position of the needle relative to the start of the haystack. Otherwise, it returns FALSE. If it does not return FALSE, the if expression evaluates to TRUE and the code within its {braces} is executed. Otherwise, the code is not run. Feel free to create similar examples, with if, else, and other functions such as strtoupper() and strlen(). Each related manual page contains examples too. If you are unsure how to use functions, you will want to read both the manual page on how to read a function definition and the section about PHP functions.
We can take this a step further and show how you can jump in and out of PHP mode even in the middle of a PHP block:
????? 2-5. Mixing both HTML and PHP modes
if (strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== FALSE) {
?>
} else {
?>
}
?>
A sample output of this script may be:
Instead of using a PHP echo statement to output something, we jumped out of PHP mode and just sent straight HTML. The important and powerful point to note here is that the logical flow of the script remains intact. Only one of the HTML blocks will end up getting sent to the viewer depending on the result of strpos(). In other words, it depends on whether the string MSIE was found or not
Let us do something more useful now. We are going to check what sort of browser the visitor is using. For that, we check the user agent string the browser sends as part of the HTTP request. This information is stored in a variable. Variables always start with a dollar-sign in PHP. The variable we are interested in right now is $_SERVER['HTTP_USER_AGENT'].
????: $_SERVER is a special reserved PHP variable that contains all web server information. It is known as an autoglobal (or superglobal). See the related manual page on superglobals for more information. These special variables were introduced in PHP 4.1.0. Before this time, we used the older $HTTP_*_VARS arrays instead, such as $HTTP_SERVER_VARS. Although deprecated, these older variables still exist. (See also the note on old code.)
To display this variable, you can simply do:
????? 2-3. Printing a variable (Array element)
A sample output of this script may be:
Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
There are many types of variables available in PHP. In the above example we printed an Array element. Arrays can be very useful.
$_SERVER is just one variable that PHP automatically makes available to you. A list can be seen in the Reserved Variables section of the manual or you can get a complete list of them by looking at the output of the phpinfo() function used in the example in the previous section.
You can put multiple PHP statements inside a PHP tag and create little blocks of code that do more than just a single echo. For example, if you want to check for Internet Explorer you can do this:
????? 2-4. Example using control structures and functions
if (strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== FALSE) {
echo 'You are using Internet Explorer.
';
}
?>
A sample output of this script may be:
You are using Internet Explorer.
Here we introduce a couple of new concepts. We have an if statement. If you are familiar with the basic syntax used by the C language, this should look logical to you. Otherwise, you should probably pick up an introductory PHP book and read the first couple of chapters, or read the Language Reference part of the manual. You can find a list of PHP books at http://www.php.net/books.php.
The second concept we introduced was the strpos() function call. strpos() is a function built into PHP which searches a string for another string. In this case we are looking for 'MSIE' (so-called needle) inside $_SERVER['HTTP_USER_AGENT'] (so-called haystack). If the needle is found inside the haystack, the function returns the position of the needle relative to the start of the haystack. Otherwise, it returns FALSE. If it does not return FALSE, the if expression evaluates to TRUE and the code within its {braces} is executed. Otherwise, the code is not run. Feel free to create similar examples, with if, else, and other functions such as strtoupper() and strlen(). Each related manual page contains examples too. If you are unsure how to use functions, you will want to read both the manual page on how to read a function definition and the section about PHP functions.
We can take this a step further and show how you can jump in and out of PHP mode even in the middle of a PHP block:
????? 2-5. Mixing both HTML and PHP modes
if (strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== FALSE) {
?>
strpos() must have returned non-false
You are using Internet Explorer
} else {
?>
strpos() must have returned false
You are not using Internet Explorer
}
?>
A sample output of this script may be:
strpos() must have returned non-false
You are using Internet Explorer
Instead of using a PHP echo statement to output something, we jumped out of PHP mode and just sent straight HTML. The important and powerful point to note here is that the logical flow of the script remains intact. Only one of the HTML blocks will end up getting sent to the viewer depending on the result of strpos(). In other words, it depends on whether the string MSIE was found or not
Your first PHP-enabled page
Create a file named hello.php and put it in your web server's root directory (DOCUMENT_ROOT) with the following content:
????? 2-1. Our first PHP script: hello.php
PHP Test
Hello World'; ?>
Use your browser to access the file with your web server's URL, ending with the "/hello.php" file reference. When developing locally this URL will be something like http://localhost/hello.php or http://127.0.0.1/hello.php but this depends on the web server's configuration. If everything is configured correctly, this file will be parsed by PHP and the following output will be sent to your browser:
PHP Test
This program is extremely simple and you really did not need to use PHP to create a page like this. All it does is display: Hello World using the PHP echo() statement. Note that the file does not need to be executable or special in any way. The server finds out that this file needs to be interpreted by PHP because you used the ".php" extension, which the server is configured to pass on to PHP. Think of this as a normal HTML file which happens to have a set of special tags available to you that do a lot of interesting things.
????? 2-1. Our first PHP script: hello.php
Hello World'; ?>
Use your browser to access the file with your web server's URL, ending with the "/hello.php" file reference. When developing locally this URL will be something like http://localhost/hello.php or http://127.0.0.1/hello.php but this depends on the web server's configuration. If everything is configured correctly, this file will be parsed by PHP and the following output will be sent to your browser:
Hello World
This program is extremely simple and you really did not need to use PHP to create a page like this. All it does is display: Hello World using the PHP echo() statement. Note that the file does not need to be executable or special in any way. The server finds out that this file needs to be interpreted by PHP because you used the ".php" extension, which the server is configured to pass on to PHP. Think of this as a normal HTML file which happens to have a set of special tags available to you that do a lot of interesting things.
what is php programming
PHP (recursive acronym for "PHP: Hypertext Preprocessor") is a widely-used Open Source general-purpose scripting language that is especially suited for Web development and can be embedded into HTML.
Simple answer, but what does that mean? An example:
Notice how this is different from a script written in other languages like Perl or C -- instead of writing a program with lots of commands to output HTML, you write an HTML script with some embedded code to do something (in this case, output some text). The PHP code is enclosed in special start and end tags that allow you to jump into and out of "PHP mode".
What distinguishes PHP from something like client-side JavaScript is that the code is executed on the server. If you were to have a script similar to the above on your server, the client would receive the results of running that script, with no way of determining what the underlying code may be. You can even configure your web server to process all your HTML files with PHP, and then there's really no way that users can tell what you have up your sleeve.
The best things in using PHP are that it is extremely simple for a newcomer, but offers many advanced features for a professional programmer. Don't be afraid reading the long list of PHP's features. You can jump in, in a short time, and start writing simple scripts in a few hours.
Although PHP's development is focused on server-side scripting, you can do much more with it. Read on, and see more in the What can PHP do? section, or go right to the introductory tutorial if you are only interested in web programming.
Subscribe to:
Posts (Atom)