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    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 $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 needle compared to the length of haystack minus the offset.

    case_insensitive

    If case_insensitive is true, comparison is case insensitive.

    Return Values

    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.

    Changelog

    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.

    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
    ?>

    See Also

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

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    User Contributed Notes 3 notes

    up
    31
    jimmetry at gmail dot com
    12 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.

    <?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);
    }

    ?>
    up
    12
    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"
    ?>
    up
    8
    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.
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