(PHP 5, PHP 7)
substr_compare — 二进制安全比较字符串（从偏移位置比较指定长度）
$main_str
, string $str
, int $offset
[, int $length
[, bool $case_insensitivity = FALSE
]] ) : int
substr_compare() 从偏移位置 offset 开始比较 main_str 与 str，比较长度为 length 个字符。
main_str待比较的第一个字符串。
str待比较的第二个字符串。
offset比较开始的位置。如果为负数，则从字符串结尾处开始算起。
length
比较的长度。默认值为 str 的长度与 main_str 的长度减去位置偏移量 offset 后二者中的较大者。
case_insensitivity
如果 case_insensitivity 为 TRUE，比较将不区分大小写。
如果 main_str 从偏移位置 offset 起的子字符串小于 str，则返回小于 0 的数；如果大于 str，则返回大于 0 的数；如果二者相等，则返回 0。如果 offset 大于等于 main_str 的长度或 length 被设置为小于 1 的值（ PHP 5.5.11 之前的版本），substr_compare() 将打印出一条警告信息并且返回 FALSE。
| 版本 | 说明 |
|---|---|
| 5.5.11 |
length 可以是 0。
|
| 5.1.0 |
允许使用负数的 offset 参数。
|
Example #1 substr_compare() 范例
<?php
echo substr_compare("abcde", "bc", 1, 2); // 0
echo substr_compare("abcde", "de", -2, 2); // 0
echo substr_compare("abcde", "bcg", 1, 2); // 0
echo substr_compare("abcde", "BC", 1, 2, true); // 0
echo substr_compare("abcde", "bc", 1, 3); // 1
echo substr_compare("abcde", "cd", 1, 2); // -1
echo substr_compare("abcde", "abc", 5, 1); // warning
?>
This function efficiently implements checks for strings beginning or ending with other strings:
<?php
function str_begins($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.
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);
}
?>
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"
?>
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);
}
}
?>