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    substr_compare

    (PHP 5, PHP 7, PHP 8)

    substr_compare — Confronto tra due stringhe a partire da una data posizione per n caratteri, sicuro con i dati binari e, opzionalmente, senza distinguere tra lettere maiuscole e minuscole

    Descrizione

    substr_compare(
        string $main_str,
        string $str,
        int $offset,
        int $length = ?,
        bool $case_insensitivity = ?
    ): int

    La funzione substr_compare() confronta main_str dalla posizione offset con la stringa str per length caratteri di lunghezza.

    Restituisce < 0 se main_str dalla posizione offset è minore di str, > 0 se è maggiore di str, e 0 se sono uguali. Se length è uguale o maggiore della lunghezza di main_str ed è impostato il parametro length, substr_compare() visualizza un warning e restituisce false.

    Se case_insensitivity è true, il confronto non distingue tra lettere maiuscole e minuscole.

    Example #1 Esempio di uso di substr_compare()

    <?php
    echo substr_compare("abcde", "bc", 1, 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
    ?>

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    User Contributed Notes 4 notes

    up
    20
    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
    6
    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.
    up
    9
    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
    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);
        }
    }
    ?>
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