Php Programming Code Examples Php > Algorithms Code Examples This function returns the position of string s1 within string s2 This function returns the position of string s1 within string s2 The position is 1 based. If s1 is not in s2, 0 is returned <?php /* This function returns the position of string s1 within string s2. The position is 1 based. If s1 is not in s2, 0 is returned. */ function InStr($s1, $s2) { //Check for valid input if(!(is_string($s1) && is_string($s2))) return 0; $s1len = strlen($s1); $s2len = strlen($s2); //Check if s1 in s2 at all if(!ereg($s1, $s2)) return 0; //Resolve simple case if($s1 == $s2) return 1; //Set initial search limits $begin = 0; $end = $s2len - $s1len; //Initialize position $position = 0; //Do binary search of s2 for s1 //Check left side first to find first occurance of s1 //Check right side first to find last occurance of s1 while($end > $begin + 1) { $middle = ceil(($begin + $end) / 2); $leftBegin = $begin; $rightBegin = $middle + $s1len; $leftEnd = $middle; $rightEnd = $end + $s1len; //Check left first if(ereg($s1, substr($s2, $leftBegin, $rightBegin - $leftBegin))) { $end = $middle; } else //(ereg($s1, substr($s2, $leftEnd, $rightEnd - $leftEnd))) { $position += $middle - $begin; $begin = $middle; } } //Resolve 1 off problems introduced by ceil if(ereg($s1, substr($s2, $end, $s1len))) $position++; //Return position 1 based return $position + 1; } ?>