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 string1 小于 string2，则返回小于 0 的值；如果 string1 大于 string2，则返回大于 0 的值；如果它们相等，则返回 0。除了它的符号外，不能从返回值中可靠推断出任何特定的含义。

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	当字符串长度不相等时，此函数不再保证返回 `strlen($string1) - strlen($string2)`，而可能返回 `-1` 或 `1`。
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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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);
}

?>

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

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.