(PHP 4, PHP 5, PHP 7, PHP 8)
strncmp — Binary safe string comparison of the first n characters
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.
string1The first string.
string2The second string.
lengthNumber of characters to use in the comparison.
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.
| 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.
|
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';
}
?>
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, $str2); // 3
?>
since str2 = "php" is a sub-string of str1 = "phpaaa" and "phpaaa" is greater than "php" the returned value is positive and is 3 indicating how many characters the difference is between the two strings.
If you replace the value of str1 with str2 the result will be -3 (negative) but still indicates the absolute difference which is 3I ran the following experiment to compare arrays.
1 st - using (substr($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)
)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
*/ ?>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);
?>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
?>