strncmp

(PHP 4, PHP 5)

strncmp — 二进制安全比较字符串开头的若干个字符

说明

int strncmp ( string $str1 , string $str2 , int $len )

该函数与 strcmp() 类似，不同之处在于你可以指定两个字符串比较时使用的长度（即最大比较长度）。

注意该比较区分大小写。

参数

str1: 第一个字符串。
str2: 第二个字符串。
len: 最大比较长度。

返回值

如果 str1 小于 str2 返回 < 0；如果 str1 大于 str2 返回 > 0；如果两者相等，返回 0。

参见

strncasecmp() - 二进制安全比较字符串开头的若干个字符（不区分大小写）
preg_match() - 执行一个正则表达式匹配
substr_compare() - 二进制安全比较字符串（从偏移位置比较指定长度）
strcmp() - 二进制安全字符串比较
strstr() - 查找字符串的首次出现
substr() - 返回字符串的子串

用户评论:

[#1] bobvin at pillars dot net [2011-05-19 07:25:15]

For checking matches at the beginning of a short string, strpos() is about 15% faster than strncmp().

Here's a benchmark program to prove it:

<?php $haystack = "abcdefghijklmnopqrstuvwxyz"; $needles = array('abc', 'xyz', '123'); foreach ($needles as $needle) { $times['strncmp'][$needle] = -microtime(true); for ($i = 0; $i < 1000000; $i++) { $result = strncmp($haystack, $needle, 3) === 0; } $times['strncmp'][$needle] += microtime(true); } foreach ($needles as $needle) { $times['strpos'][$needle] = -microtime(true); for ($i = 0; $i < 1000000; $i++) { $result = strpos($haystack, $needle) === 0; } $times['strpos'][$needle] += microtime(true); } var_export($times); ?>

[#2] elloromtz at gmail dot com [2010-04-19 05:25:33]

if length is 0 regardless what the two strings are, it will return 0

<?php strncmp("xybc","a3234",0); // 0 strncmp("blah123","hohoho", 0); //0 ?>

[#3] codeguru at crazyprogrammer dot cba dot pl [2008-01-24 11:07:50]

I ran the following experiment to compare arrays.

1 st - using (substr($key,0,5 == "HTTP_") & 2 nd - using (!strncmp($key, 'HTTP_', 5))

I wanted to work out the fastest way to get the first few characters from a array

BENCHMARK ITERATION RESULT IS:
if (substr($key,0,5 == "HTTP_").... -   0,000481s
if (!strncmp($key, 'HTTP_', 5)).... - 0,000405s

strncmp() is 20% faster than substr() :D

<?php // SAMPLE FUNCTION function strncmp_match($arr) { foreach ($arr as $key => $val)     {     //if (substr($key,0,5 == "HTTP_")     if (!strncmp($key, 'HTTP_', 5))             {     $out[$key] = $val;         }     } return $out; } // EXAMPLE USE ?><pre><?php print_r(strncmp_match($_SERVER)); ?></pre>

will display code like this:

Array
(
    [HTTP_ACCEPT] => XXX
    [HTTP_ACCEPT_LANGUAGE] => pl
    [HTTP_UA_CPU] => x64
    [HTTP_ACCEPT_ENCODING] => gzip, deflate
    [HTTP_USER_AGENT] => Mozilla/4.0
                                    (compatible; MSIE 7.0;
                                     Windows NT 5.1;
                                    .NET CLR 1.1.4322;
                                    .NET CLR 2.0.50727)
    [HTTP_HOST] => XXX.XXX.XXX.XXX
    [HTTP_CONNECTION] => Keep-Alive
    [HTTP_COOKIE] => __utma=XX;__utmz=XX.utmccn=(direct)|utmcsr=(direct)|utmcmd=(none)
)