substr_compare

(PHP 5, PHP 7, PHP 8)

substr_compare — 二进制安全比较字符串（从偏移位置比较指定长度）

说明

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

substr_compare() 从偏移位置 offset 开始比较 haystack 与 needle，比较长度为 length 个字符。

参数

haystack: 待比较的第一个字符串。
needle: 待比较的第二个字符串。
offset: 比较开始的位置。如果为负数，则从字符串结尾处开始算起。
length: 比较的长度。默认值为 needle 的长度与 haystack 的长度减去位置偏移量 offset 后二者中的较大者。
case_insensitive: 如果 case_insensitive 为 true，比较将不区分大小写。

返回值

如果 haystack 从偏移位置 offset 起的子字符串小于 needle，则返回 -1；如果大于 needle，则返回 1；如果二者相等，则返回 0。如果 offset 等于（在 PHP 7.2.18, 7.3.5 之前）或大于 haystack 的长度，或设置 length 小于或等于 0，substr_compare() 将打印出警告信息并且返回 false。

更新日志

版本	说明
8.2.0	现在此函数返回 `-1` 或者 `1`，之前返回负数或正数。
8.0.0	`length` 现在允许为 null。
7.2.18, 7.3.5	`offset` 现在可能等于 `haystack`。

示例

示例 #1 substr_compare() 示例

<?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
?>

参见

strncmp() - 二进制安全比较字符串开头的若干个字符

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User Contributed Notes 4 notes

down

jimmetry at gmail dot com ¶

10 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

Skyborne ¶

11 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

bishop at php dot net ¶

7 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

-14

sleek ¶

18 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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