(PHP 5, PHP 7, PHP 8)
substr_compare — Binary safe comparison of two strings from an offset, up to length characters
$haystack,$needle,$offset,$length = null ,$case_insensitive = false
substr_compare() compares haystack
from position offset with needle
up to length characters.
haystackThe main string being compared.
needleThe secondary string being compared.
offsetThe start position for the comparison. If negative, it starts counting from the end of the string.
length
The length of the comparison. The default value is the largest of the
length of the needle compared to the length of
haystack minus the
offset.
case_insensitive
If case_insensitive is true , comparison is
case insensitive.
Returns a value less than 0 if string1
is less than string2; a value greater
than 0 if string1 is greater than
string2, and 0 if they
are equal.
No particular meaning can be reliably inferred from the value aside
from its sign.
If offset is equal to (prior to PHP 7.2.18, 7.3.5) or
greater than the length of haystack, or the
length is set and is less than 0,
substr_compare() prints a warning and returns
false .
| Version | Description |
|---|---|
| 8.2.0 |
This function is no longer guaranteed to return
strlen($string1) - strlen($string2) when string lengths
are not equal, but may now return -1 or
1 instead.
|
| 8.0.0 |
length is nullable now.
|
| 7.2.18, 7.3.5 |
offset may now be equal to the length of haystack.
|
Example #1 A substr_compare() example
<?php
echo substr_compare("abcde", "bc", 1, 2), PHP_EOL; // 0
echo substr_compare("abcde", "de", -2, 2), PHP_EOL; // 0
echo substr_compare("abcde", "bcg", 1, 2), PHP_EOL; // 0
echo substr_compare("abcde", "BC", 1, 2, true), PHP_EOL; // 0
echo substr_compare("abcde", "bc", 1, 3), PHP_EOL; // 1
echo substr_compare("abcde", "cd", 1, 2), PHP_EOL; // -1
echo substr_compare("abcde", "abc", 5, 1), PHP_EOL; // -1
?>When you came to this page, you may have been looking for something a little simpler: A function that can check if a small string exists within a larger string starting at a particular index. Using substr_compare() for this can leave your code messy, because you need to check that your string is long enough (to avoid the warning), manually specify the length of the short string, and like many of the string functions, perform an integer comparison to answer a true/false question.
I put together a simple function to return true if $str exists within $mainStr. If $loc is specified, the $str must begin at that index. If not, the entire $mainStr will be searched.
<?php
function contains_substr($mainStr, $str, $loc = false) {
if ($loc === false) return (strpos($mainStr, $str) !== false);
if (strlen($mainStr) < strlen($str)) return false;
if (($loc + strlen($str)) > strlen($mainStr)) return false;
return (strcmp(substr($mainStr, $loc, strlen($str)), $str) == 0);
}
?>This function efficiently implements checks for strings beginning or ending with other strings:
<?php
function str_begins($haystack, $needle) {
return 0 === substr_compare($haystack, $needle, 0, strlen($needle));
}
function str_ends($haystack, $needle) {
return 0 === substr_compare($haystack, $needle, -strlen($needle));
}
var_dump(str_begins('http://example.com', 'https://'));
?>
Note that these are not multi-byte character set aware.Take note of the `length` parameter: "The default value is the largest of the length of the str compared to the length of main_str less the offset."
This is *not* the length of str as you might (I always) expect, so if you leave it out, you'll get unexpected results. Example:
<?php
$hash = '5ドル$lalalalalalalala$crypt.output.here';
var_dump(substr_compare($hash, '5ドル$', 0)); # int(34)
var_dump(substr_compare($hash, '5ドル$', 0, 3)); # int(0)
var_dump(PHP_VERSION); # string(6) "5.3.14"
?>