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    strncmp

    (PHP 4, PHP 5, PHP 7)

    strncmp — 처음 n 문자의 바이너리 안전 문자열 비교

    설명

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

    이 함수는 비교에 사용하는 각 문자열에 (최대 제한) 비교에 사용할 문자 수를 지정할 수 있는 점을 제외하면, strcmp()와 동일합니다.

    이 비교는 대소문자를 구분합니다.

    인수

    str1

    첫번째 문자열.

    str2

    두번째 문자열.

    len

    비교에 사용할 문자열의 길이.

    반환값

    str1이 str2보다 작으면 < 0을; str1이 str2보다 크면 > 0을, 같으면 0을 반환합니다.

    참고

    • preg_match() - 정규표현식 매치를 수행
    • strcmp() - 바이너리 안전 문자열 비교
    • strcasecmp() - 대소문자 구분 없는 바이너리 안전 문자열 비교
    • substr() - Return part of a string
    • stristr() - 대소문자를 구분하지 않는 strstr
    • strncasecmp() - 대소문자 구분 없는 처음 n 문자의 바이너리 안전 문자열 비교
    • strstr() - 문자열이 처음으로 나오는 부분을 찾습니다

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    User Contributed Notes 5 notes

    up
    8
    salehrezq at gmail dot com
    7 years ago
    A note not included in the documentation:

    int strcmp ( string $str1 , string $str2 )

    Returns < 0 if str1 is less than str2; > 0 if str1 is greater than str2, and 0 if they are equal.

    My addendum:
    If str1 and str2 are not equal, and str1 is a sub-string of str2 or vise versa. The returned int value will be negative or positive indicating how many characters the difference is between the two strings in absolute terms.

    Example:

    <?php
    $str1     = "phpaaa";
    $str2 = "php";

    echo     strcmp($str1, $str2); // 3
    ?>

    since str2 = "php" is a sub-string of str1 = "phpaaa" and "phpaaa" is greater than "php" the returned value is positive and is 3 indicating how many characters the difference is between the two strings.

    If you replace the value of str1 with str2 the result will be -3 (negative) but still indicates the absolute difference which is 3
    up
    7
    codeguru at crazyprogrammer dot cba dot pl
    16 years ago
    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)
    )
    up
    3
    samy
    6 years ago
    I just want to highlight that (at least on php7), when testing for the existence of a string in the beginning of another string you should consider using substr  or strpos (if performances is an issue).

    Here is a small benchmark (for what it's worth):
    <?php
    $n     = 'abcd';
    $l = strlen($n);
    $haystack0 = base64_encode(random_bytes(128));

    //heat
    $r = 1;
    for (    $i = 0; $i < 100000000; $i++)
            $r += $r * $r % 10000;

    //tests
    $k = 30000000;
    $res = array();
    foreach (array(    'found' => $n . $haystack0, 'not-found' => strrev($n) . $haystack0) as $f => $haystack) {
            $m = microtime(true);
        for (    $i = 0; $i < $k; $i++)
            !    strncmp($haystack, $n, $l) && $r++;
            $res["strncmp-$f"] = -$m + ($m = microtime(true));

        for (    $i = 0; $i < $k; $i++)
            (    strpos($haystack, $n) === 0) && $r++;
            $res["strpos-$f"] = -$m + ($m = microtime(true));

        for (    $i = 0; $i < $k; $i++)
            (    substr($haystack, 0, $l) === $n) && $r++;
            $res["substr-$f"] = microtime(true) - $m;
    }

    //print
    asort($res);
    print_r($res);
    echo     "\n$r"; // makes sure no auto-optimization occurs
    ?>

    This outputs:
    <?php /*
        [strpos-found]        => 1.3313138484955
        [substr-not-found]    => 1.4832630157471
        [substr-found]        => 1.6976611614227
        [strpos-not-found]    => 2.0043320655823
        [strncmp-not-found]    => 2.0969619750977
        [strncmp-found]        => 2.3616981506348
    */     ?>
    up
    2
    bobvin at pillars dot net
    12 years ago
    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);
    ?>
    up
    2
    elloromtz at gmail dot com
    14 years ago
    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
    ?>
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