(PHP 4, PHP 5)
strncmp — 二进制安全比较字符串开头的若干个字符
$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。
str1
第一个字符串。
str2
第二个字符串。
len
最大比较长度。
如果 str1 小于 str2，返回负数；如果 str1 大于 str2，返回正数；二者相等则返回 0。
Anonymous (2013-01-30 14:07:56)
Returns FALSE if $len is negative or NAN.
Floating point values for $len are rounded towards 0.
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($times);
?>
elloromtz at gmail dot com (2010-04-19 05:25:33)
if length is 0 regardless what the two strings are, it will return 0
<?php
strncmp("xybc","a3234",0); // 0
strncmp("blah123","hohoho", 0); //0
?>
codeguru at crazyprogrammer dot cba dot pl (2008-01-24 11:07:50)
I ran the following experiment to compare arrays.
1 st - using (substr($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)
)
Anonymous (2002-04-17 04:46:15)
strncmp("sample","sam",4) returns 1 because the final requirement is if one string terminates before len, then the other must also terminate at that position.
You can imagine that all your strings have one more final, invisible "termination" character. If that termination character happens to be within in len, then it must match, too.
For instance, write that termination character with, say, the sequence "\0". Then you can equivalently consider that function call as strncmp("sample\0","sam\0",4).
So, the "p" in "sample" does not match the termination character in "sam".