PHP 8.5.0 Alpha 1 available for testing

strncmp

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

strncmpComparación binaria de los n primeros caracteres

Descripción

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

Idéntica a la función strcmp(), con la diferencia de que se puede especificar el número máximo de caracteres a utilizar para la comparación de string1 con string2 mediante el parámetro length.

Tenga en cuenta que esta comparación es sensible a mayúsculas y minúsculas.

Parámetros

string1

El primer string.

string2

El segundo string.

length

Número de caracteres a utilizar para la comparación.

Valores devueltos

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.

Historial de cambios

Versión Descripción
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.

Ejemplos

Ejemplo #1 Ejemplo con strncmp()

<?php

$var1
= 'Hello John';
$var2 = 'Hello Doe';
if (
strncmp($var1, $var2, 5) === 0) {
echo
'Los 5 primeros caracteres de $var1 y $var2 son iguales en una comparación de strings sensibles a mayúsculas y minúsculas.';
}
?>

Ver también

  • strncasecmp() - Comparación binaria de strings insensible a mayúsculas/minúsculas
  • preg_match() - Realiza una búsqueda de coincidencia con una expresión regular estándar
  • substr_compare() - Comparar dos strings desde un offset hasta una longitud en caracteres
  • strcmp() - Comparación binaria de strings
  • strstr() - Encuentra la primera ocurrencia en un string
  • substr() - Devuelve un segmento de string

add a note

User Contributed Notes 5 notes

up
10
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
up
9
codeguru at crazyprogrammer dot cba dot pl
17 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
4
samy
8 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
4
bobvin at pillars dot net
14 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
4
elloromtz at gmail dot com
15 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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