strnatcmp

Description

int strnatcmp ( string str1, string str2 )

This function implements a comparison algorithm that orders alphanumeric strings in the way a human being would, this is described as a "natural ordering". An example of the difference between this algorithm and the regular computer string sorting algorithms (used in strcmp()) can be seen below:


<?php
$arr1 = $arr2 = array("img12.png", "img10.png", "img2.png", "img1.png");
echo "Standard string comparison\n";
usort($arr1, "strcmp");
print_r($arr1);
echo "\nNatural order string comparison\n";
usort($arr2, "strnatcmp");
print_r($arr2);
?>

The code above will generate the following output:

Standard string comparison
Array
(
    [0] => img1.png
    [1] => img10.png
    [2] => img12.png
    [3] => img2.png
)

Natural order string comparison
Array
(
    [0] => img1.png
    [1] => img2.png
    [2] => img10.png
    [3] => img12.png
)

For more information see: Martin Pool's Natural Order String Comparison page.

Similar to other string comparison functions, this one returns < 0 if str1 is less than str2; > 0 if str1 is greater than str2, and 0 if they are equal.

Note that this comparison is case sensitive.

add a note User Contributed Notes

thomas at uninet dot se
25-Jul-2006 03:50


There seems to be a bug in the localization for strnatcmp and strnatcasecmp. I searched the reported bugs and found a few entries which were up to four years old (but the problem still exists when using swedish characters).



These functions might work instead.

<?php

function _strnatcasecmp($left, $right) {

  return _strnatcmp(strtolower($left), strtolower($right));

}



function _strnatcmp($left, $right) {

  while((strlen($left) > 0) && (strlen($right) > 0)) {

    if(preg_match('/^([^0-9]*)([0-9].*)$/Us', $left, $lMatch)) {

      $lTest = $lMatch[1];

      $left = $lMatch[2];

    } else {

      $lTest = $left;

      $left = '';

    }

    if(preg_match('/^([^0-9]*)([0-9].*)$/Us', $right, $rMatch)) {

      $rTest = $rMatch[1];

      $right = $rMatch[2];

    } else {

      $rTest = $right;

      $right = '';

    }

    $test = strcmp($lTest, $rTest);

    if($test != 0) {

      return $test;

    }

    if(preg_match('/^([0-9]+)([^0-9].*)?$/Us', $left, $lMatch)) {

      $lTest = intval($lMatch[1]);

      $left = $lMatch[2];

    } else {

      $lTest = 0;

    }

    if(preg_match('/^([0-9]+)([^0-9].*)?$/Us', $right, $rMatch)) {

      $rTest = intval($rMatch[1]);

      $right = $rMatch[2];

    } else {

      $rTest = 0;

    }

    $test = $lTest - $rTest;

    if($test != 0) {

      return $test;

    }

  }

  return strcmp($left, $right);

}

?>



The code is not optimized. It was just made to solve my problem.

public at macfreek dot nl
15-Aug-2002 10:03


The URI of Martin Pool's page is http://sourcefrog.net/projects/natsort/

(Yes, that's frog, not forge).



http://www.naturalordersort.org/ points to a page with the same idea, by Stuart Cheshire, who wrote a small Mac extension to do natural sorting.

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