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.