Simple way to implement this function in PHP 4

<?php
if (function_exists('strripos') == false) {
    function strripos($haystack, $needle) {
        return strlen($haystack) - strpos(strrev($haystack), $needle);
    }
}

?>

Suppose you just need a stripos function working backwards expecting that strripos does this job, you better use the following code of a custom function named strbipos:

<?php
function strbipos($haystack="", $needle="", $offset=0) {
// Search backwards in $haystack for $needle starting from $offset and return the position found or false

    $len = strlen($haystack);
    $pos = stripos(strrev($haystack), strrev($needle), $len - $offset - 1);
    return ( ($pos === false) ? false : $len - strlen($needle) - $pos );
}

// Test
$body = "01234Xy7890XYz456xy90";
$str = "xY";
$len = strlen($body);
echo "TEST POSITIVE offset VALUES IN strbipos<br>";
for ($i = 0; $i < $len; $i++) {
    echo "Search in [$body] for [$str] starting from offset [$i]: [" . strbipos($body, $str, $i) . "]<br>";
}
?>

Note that this function does exactly what it says and its results are different comparing to PHP 5 strripos function.

I think you shouldn't underestimate the length of $needle in the search of THE FIRST POSITION of it's last occurrence in the string. I improved the posted function, with added support for offset. I think this is an exact copy of the real function:

<?php
if(!function_exists("strripos")){
    function strripos($haystack, $needle, $offset=0) {
        if($offset<0){
            $temp_cut = strrev(  substr( $haystack, 0, abs($offset) )  );
        }
        else{
            $temp_cut = strrev(  substr( $haystack, $offset )  );
        }
        $pos = strlen($haystack) - (strpos($temp_cut, strrev($needle)) + $offset + strlen($needle));
        if ($pos == strlen($haystack)) { $pos = 0; }
        return $pos;
    }/* endfunction strripos*/
}/* endfunction exists strripos*/
?>

OK, I guess this will be the final function implementation for PHP 4.x versions ( my previous posts are invalid )

<?php

if(!function_exists("stripos")){
    function stripos(  $str, $needle, $offset = 0  ){
        return strpos(  strtolower( $str ), strtolower( $needle ), $offset  );
    }/* endfunction stripos */
}/* endfunction exists stripos */

if(!function_exists("strripos")){
    function strripos(  $haystack, $needle, $offset = 0  ) {
        if(  !is_string( $needle )  )$needle = chr(  intval( $needle )  );
        if(  $offset < 0  ){
            $temp_cut = strrev(  substr( $haystack, 0, abs($offset) )  );
        }
        else{
            $temp_cut = strrev(    substr(   $haystack, 0, max(  ( strlen($haystack) - $offset ), 0  )   )    );
        }
        if(   (  $found = stripos( $temp_cut, strrev($needle) )  ) === FALSE   )return FALSE;
        $pos = (   strlen(  $haystack  ) - (  $found + $offset + strlen( $needle )  )   );
        return $pos;
    }/* endfunction strripos */
}/* endfunction exists strripos */
?>

Generally speaking, linear searches are from start to end, not end to start - which makes sense from a human perspective. If you need to find strings in a string backwards, reverse your haystack and needle rather than manually chopping it up.

Sorry, I made that last post a bit prematurely.  One more thing wrong with the simple php4 version is that it breaks if the string is not found.  It should actually look like this:

<?php
if (function_exists('strripos') == false) {
    function strripos($haystack, $needle) {
        $pos = strlen($haystack) - strpos(strrev($haystack), strrev($needle));
        if ($pos == strlen($haystack)) { $pos = 0; }
        return $pos;
    }
}
?>

Note, we now check to see if the $needle was found, and if it isn't, we return 0.