strncmp

(PHP 4, PHP 5)

strncmp — 最初の n 文字についてバイナリセーフな文字列比較を行う

説明

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

この関数は strcmp() に似ていますが、各文字列から(最大)文字数(len) を比較に使用するところが異なります。

比較は大文字小文字を区別することに注意してください。

パラメータ

str1: 最初の文字列。
str2: 次の文字列。
len: 比較する文字数。

返り値

str1 が str2 より小さい場合に < 0、str1 が str2 より大きい場合に > 0 、等しい場合に 0 を返します。

参考

strncasecmp() - バイナリセーフで大文字小文字を区別しない文字列比較を、最初の n 文字について行う
preg_match() - 正規表現によるマッチングを行う
substr_compare() - 指定した位置から指定した長さの 2 つの文字列について、バイナリ対応で比較する
strcmp() - バイナリセーフな文字列比較
strstr() - 文字列が最初に現れる位置を見つける
substr() - 文字列の一部分を返す

strpbrk

strncasecmp

[edit] Last updated: Fri, 10 Feb 2012

add a note User Contributed Notes strncmp

bobvin at pillars dot net 19-May-2011 01:25


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 18-Apr-2010 11:25


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 24-Jan-2008 04:07


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 16-Apr-2002 10:46


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".

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