SunshinePHP 2016


(PHP 5)

substr_compareBinary safe comparison of two strings from an offset, up to length characters


int substr_compare ( string $main_str , string $str , int $offset [, int $length [, bool $case_insensitivity = false ]] )

substr_compare() compares main_str from position offset with str up to length characters.



The main string being compared.


The secondary string being compared.


The start position for the comparison. If negative, it starts counting from the end of the string.


The length of the comparison. The default value is the largest of the length of the str compared to the length of main_str less the offset.


If case_insensitivity is TRUE, comparison is case insensitive.

Zwracane wartości

Returns < 0 if main_str from position offset is less than str, > 0 if it is greater than str, and 0 if they are equal. If offset is equal to or greater than the length of main_str or length is set and is less than 1, substr_compare() prints a warning and returns FALSE.

Rejestr zmian

Wersja Opis
5.1.0 Added the possibility to use a negative offset.


Przykład #1 A substr_compare() example

echo substr_compare("abcde""bc"12); // 0
echo substr_compare("abcde""de", -22); // 0
echo substr_compare("abcde""bcg"12); // 0
echo substr_compare("abcde""BC"12true); // 0
echo substr_compare("abcde""bc"13); // 1
echo substr_compare("abcde""cd"12); // -1
echo substr_compare("abcde""abc"51); // warning

Zobacz też:

  • strncmp() - Binary safe string comparison of the first n characters

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User Contributed Notes 3 notes

jimmetry at gmail dot com
2 years ago
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.


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);

3 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:

= '$5$lalalalalalalala$';
var_dump(substr_compare($hash, '$5$', 0)); # int(34)
var_dump(substr_compare($hash, '$5$', 0, 3)); # int(0)
var_dump(PHP_VERSION); # string(6) "5.3.14"
10 years ago
Modified version of the original posted function. Use this one:

if (!function_exists('substr_compare')) {
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);

// 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) && $case_insensitivity === true) {
strncasecmp($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 ($case_insensitivity === true) {
strcasecmp($main_substr, $str_substr);

// Return a case-sensitive comparison of the two strings
return strcmp($main_substr, $str_substr);
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