(PHP 4, PHP 5, PHP 7, PHP 8)
strcasecmp — 二进制安全比较字符串（不区分大小写）
二进制安全比较字符串（不区分大小写）。比较不会注意区域；只有 ASCII 字母以不区分大小写的方式进行比较。
string1第一个字符串
string2第二个字符串
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。
| 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。
|
示例 #1 strcasecmp() 示例
<?php
$var1 = "Hello";
$var2 = "hello";
if (strcasecmp($var1, $var2) == 0) {
echo '$var1 is equal to $var2 in a case-insensitive string comparison';
}
?>
A simple multibyte-safe case-insensitive string comparison:
<?php
function mb_strcasecmp($str1, $str2, $encoding = null) {
if (null === $encoding) { $encoding = mb_internal_encoding(); }
return strcmp(mb_strtoupper($str1, $encoding), mb_strtoupper($str2, $encoding));
}
?>
Caveat: watch out for edge cases like "ß".The sample above is only true on some platforms that only use a simple 'C' locale, where individual bytes are considered as complete characters that are converted to lowercase before being differentiated.
Other locales (see LC_COLLATE and LC_ALL) use the difference of collation order of characters, where characters may be groups of bytes taken from the input strings, or simply return -1, 0, or 1 as the collation order is not simply defined by comparing individual characters but by more complex rules.
Don't base your code on a specific non null value returned by strcmp() or strcasecmp(): it is not portable. Just consider the sign of the result and be sure to use the correct locale!Don't forget this is a single-byte function: in Unicode strings it'll provide incoherent results as soon as both strings differ only in case. There doesn't seem to exist a built-in multi-byte alternative so you need to write your own, taking into account both character encoding and collation.I didn't see any explanation in the documentation as to precisely how the positive/negative return values are calculated for unequal strings.
After a bit of experimentation it appears that it's the difference in alphabetical position of the first character in unequal strings.
For example, the letter 'z' is the 26th letter while the letter 'a' is the 1st letter:
<?php
$zappl = "zappl";
$apple = "apple";
echo strcasecmp($zappl, $apple); #outputs 25 [26 - 1]
echo strcasecmp($apple, $zappl); #outputs -25 [1 - 26]
?>
This might be incredibly obvious to most people, but hopefully it will clarify the calculation process for some others.