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);
}
?>
substr_compare
(PHP 5, PHP 7, PHP 8)
substr_compare — Binary safe comparison of two strings from an offset, up to length characters
Description
substr_compare(
string
string
int
?int
bool
): int
string
$haystack,string
$needle,int
$offset,?int
$length = null,bool
$case_insensitive = false): int
substr_compare() compares haystack
from position offset with needle
up to length characters.
Parameters
-
haystack -
The main string being compared.
-
needle -
The secondary string being compared.
-
offset -
The start position for the comparison. If negative, it starts counting from the end of the string.
-
length -
The length of the comparison. The default value is the largest of the length of the
needlecompared to the length ofhaystackminus theoffset. -
case_insensitive -
If
case_insensitiveistrue, comparison is case insensitive.
Return Values
Returns -1 if haystack from position
offset is less than needle, 1
if it is greater than needle, and 0 if they are equal.
If offset is equal to (prior to PHP 7.2.18, 7.3.5) or
greater than the length of haystack, or the
length is set and is less than 0,
substr_compare() prints a warning and returns
false.
Changelog
| Version | Description |
|---|---|
| 8.2.0 |
This function now returns -1 or 1,
where it previously returned a negative or positive number.
|
| 8.0.0 |
length is nullable now.
|
| 7.2.18, 7.3.5 |
offset may now be equal to the length of haystack.
|
Examples
Example #1 A substr_compare() example
<?php
echo substr_compare("abcde", "bc", 1, 2); // 0
echo substr_compare("abcde", "de", -2, 2); // 0
echo substr_compare("abcde", "bcg", 1, 2); // 0
echo substr_compare("abcde", "BC", 1, 2, true); // 0
echo substr_compare("abcde", "bc", 1, 3); // 1
echo substr_compare("abcde", "cd", 1, 2); // -1
echo substr_compare("abcde", "abc", 5, 1); // warning
?>
add a note
User Contributed Notes 4 notes
jimmetry at gmail dot com ¶
11 years ago
bishop at php dot net ¶
8 years ago
This function efficiently implements checks for strings beginning or ending with other strings:
<?php
function str_begins($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.
Skyborne ¶
12 years ago
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 = '$5$lalalalalalalala$crypt.output.here';
var_dump(substr_compare($hash, '$5$', 0)); # int(34)
var_dump(substr_compare($hash, '$5$', 0, 3)); # int(0)
var_dump(PHP_VERSION); # string(6) "5.3.14"
?>
sleek ¶
19 years ago
Modified version of the original posted function. Use this one:
<?php
if (!function_exists('substr_compare')) {
function substr_compare($main_str, $str, $offset, $length = NULL, $case_insensitivity = false) {
$offset = (int) $offset;
// Throw a warning because the offset is invalid
if ($offset >= strlen($main_str)) {
trigger_error('The start position cannot exceed initial string length.', E_USER_WARNING);
return false;
}
// We are comparing the first n-characters of each string, so let's use the PHP function to do it
if ($offset == 0 && is_int($length) && $case_insensitivity === true) {
return strncasecmp($main_str, $str, $length);
}
// Get the substring that we are comparing
if (is_int($length)) {
$main_substr = substr($main_str, $offset, $length);
$str_substr = substr($str, 0, $length);
} else {
$main_substr = substr($main_str, $offset);
$str_substr = $str;
}
// Return a case-insensitive comparison of the two strings
if ($case_insensitivity === true) {
return strcasecmp($main_substr, $str_substr);
}
// Return a case-sensitive comparison of the two strings
return strcmp($main_substr, $str_substr);
}
}
?>
