getting a substring(charset independent) between given two offsets - php

Question

I just want to know if there is any built in php function where I can get a substring between given two keywords (keyword1 and keyword2). Note that keywords may repeat in the string so I must be able to get the substring between xth keyword1 and yth keyword2. Moreover, I mainly use unicode characters so the function should be charset independen.
Please help me out to handle this problem.
E.g. $string=This is their cat with a hat in the theater.
$keyword1="is"; $keyword2="the";
Task: how to get substring between 2nd occurance of "is" and 3nd occurance of "the" in the given string above.
Answer: " the cat with a hat in the "

Answer 1

You can use regular expressions:
$string = "This is their cat with a hat in the theater";
$regex1 = "/.*? is |^is/";
$regex2 = "/ the .*| the$/";
echo preg_replace($regex1, '', preg_replace($regex2, ' the', $string));
EDIT Here is more generic code:
function find($text, $str, $offset) {
$len = strlen($text);
$search_len = strlen($str);
$count = 0;
for ($i=0; $i<$len; ++$i) {
if (substr($text, $i, $search_len) == $str) {
if (++$count == $offset) {
return $i;
}
}
}
return -1;
}
function between($text, $word1, $offset1, $word2, $offset2) {
$start = find($text, $word1, $offset1);
$end = find($text, $word2, $offset2);
if ($start != -1 && $end != -1) {
return substr($text, $start + strlen($word1), $end-$start-strlen($word2));
} else {
return '';
}
}
$string = "This is their cat with a hat in the theater";
echo between($string, 'is', 2, 'the', 3);
echo between($string, 'at', 1, 'at', 3);

Answer 2

Combination of following two functions work for any string including unicode characters:
//Gets the position of a given substring with its offset;
function strposOffset($string, $search, $offset)
{
/*** explode the string ***/
$arr = explode($search, $string);
/*** check the search is not out of bounds ***/
switch( $offset )
{
case $offset == 0:
return false;
break;
case $offset > max(array_keys($arr)):
return false;
break;
default:
return mb_strlen(implode($search, array_slice($arr, 0, $offset)), "utf-8");
}
} //Source: www.phpro.org
//Extracts a substring between given two given substrings with their offsets.
function extractMiddleSubstr($string, $substr1, $offset1, $substr2, $offset2){
$strlen_substr1 = mb_strlen($substr1, "utf-8"); //length of substr1;
$strpos_substr1 = strposOffset($string, $substr1, $offset1); //position of substr1;
$strpos_substr2 = strposOffset($string, $substr2, $offset2); //position of substr2;
if($strpos_substr1!==null && $strpos_substr2!==null && $strpos_substr1!==false && $strpos_substr2!==false){
if($strpos_substr1<=$strpos_substr2){
$strpos_substr = $strlen_substr1+$strpos_substr1; //position of substr;
$strlen_substr = $strpos_substr2-$strpos_substr; //length of substr;
$substr = mb_substr($string, $strpos_substr, $strlen_substr, "utf-8"); //substr;
$substr = trim($substr); // removes whitespaces;
return $substr;
}else{
return false;
}
}else{
return false;
}
}