strncmp

(PHP 4, PHP 5, PHP 7, PHP 8)

strncmp — Binary safe string comparison of the first n characters

Description

strncmp(string $string1, string $string2, int $length): int

This function is similar to strcmp(), with the difference that you can specify the (upper limit of the) number of characters from each string to be used in the comparison.

Note that this comparison is case sensitive.

Parameters

string1: The first string.
string2: The second string.
length: Number of characters to use in the comparison.

Return Values

Returns a value less than 0 if string1 is less than string2; a value greater than 0 if string1 is greater than string2, and 0 if they are equal. No particular meaning can be reliably inferred from the value aside from its sign.

Changelog

Version	Description
8.2.0	This function is no longer guaranteed to return `strlen($string1) - strlen($string2)` when string lengths are not equal, but may now return `-1` or `1` instead.

Examples

Example #1 strncmp() example

<?php

$var1 = 'Hello John';
$var2 = 'Hello Doe';
if (strncmp($var1, $var2, 5) === 0) {
    echo 'First 5 characters of $var1 and $var2 are equal in a case-sensitive string comparison';
}
?>

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User Contributed Notes 5 notes

down

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)
)

down

salehrezq at gmail dot com ¶

8 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

down

samy ¶

7 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
*/ ?>

down

bobvin at pillars dot net ¶

13 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);

?>

down

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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strncmp

Description

Parameters

Return Values

Changelog

Examples

See Also

Found A Problem?

User Contributed Notes 5 notes