substr_compare

(PHP 5, PHP 7)

substr_compare — Binary safe comparison of two strings from an offset, up to length characters

Descrierea

substr_compare ( string $haystack , string $needle , int $offset , int|null $length = null , bool $case_insensitive = false ) : int

substr_compare() compares haystack from position offset with needle up to length characters.

Parametri

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.

Valorile întoarse

Returns < 0 if haystack from position offset is less than needle, > 0 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.

Istoricul schimbărilor

Versiune	Descriere
8.0.0	`length` is nullable now.
7.2.18, 7.3.5	`offset` may now be equal to the length of `haystack`.

Exemple

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
?>

A se vedea și

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

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User Contributed Notes 4 notes

down

jimmetry at gmail dot com ¶

11 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);
}

?>

down

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.

down

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"
?>

down

-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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