Question

I’ve used preg_match_all’s PREG_PATTERN_ORDER to return positions in the values found in a string. Then when trying to substr, referencing them back, they don’t line up. I expected an offset, but there seems to be an undetermined misalignment per case.

Is this because preg_match_all is returning bytes and not characters? If so, is there a way to convert bytes to characters? If I’m completely off the mark I can post some code…

Okay here is the applicable code:

// RETURN POSITION OF START AND END TAGS TO ARRAY
function getTagPositions($strBody, $start, $end)
{
    preg_match_all('/' . preg_quote($start, '/') . '([\w\s.]*?)'. preg_quote($end, '/').'/im', $strBody, $strTag, PREG_PATTERN_ORDER);
    $intOffset = 0;
    $intIndex = 0;
    $intTagPositions = array();

    foreach($strTag[0] as $strFullTag) {
        $intTagPositions[$intIndex] = array('start' => (strpos($strBody, $strFullTag, $intOffset)), 'end' => (strpos($strBody, $strFullTag, $intOffset) + strlen($strFullTag)));
        $intOffset += strlen($strFullTag);
        $intIndex++;
    }
    return $intTagPositions;
}

function arrayValRecursive($key, array $arr){
    $val = array();
    array_walk_recursive($arr, function($v, $k) use($key, &$val){
        if($k == $key) array_push($val, $v);
    });
    return count($val) > 1 ? $val : array_pop($val);
}

$arrayOfPositions = getTagPositions($html,$go,$stop);
$arrayOfStart = arrayValRecursive('start', $arrayOfPositions);   //print_r($arrayOfStart);
$arrayOfEnd = arrayValRecursive('end', $arrayOfPositions);   //print_r($arrayOfEnd);

  $offset = 0;
  $range = $arrayOfStart[$i] + $offset;
  $rangeEnd = $arrayOfEnd[$i];    
  echo '<br>'.$range.' to '.$rangeEnd.' is: <br>'; 
  echo substr($html, $range, $rangeEnd); 

Answer 1

According to preg_match_all

Return Values
Returns the number of full pattern matches (which might be zero), or FALSE if an error occurred.

If you want to get offsets into the string, use PREG_OFFSET_CAPTURE

PREG_OFFSET_CAPTURE
If this flag is passed, for every occurring match the appendant string offset will also be returned. Note that this changes the value of matches into an array where every element is an array consisting of the matched string at offset 0 and its string offset into subject at offset 1.

Here’s an example:

$count = preg_match_all('/\S+/', 'Hello, world!', $matches, PREG_OFFSET_CAPTURE);
echo "count=$count\n";
var_dump($matches);

This gives as output

count=2
array(1) {
  [0]=>
  array(2) {
    [0]=>
    array(2) {
      [0]=>
      string(6) "Hello,"
      [1]=>
      int(0)
    }
    [1]=>
    array(2) {
      [0]=>
      string(6) "world!"
      [1]=>
      int(7)
    }
  }
}

You can see the pattern matches $count=2 times. It matches “Hello,” at position $matches[0][0][1]=0 and it matches “world!” at position $matches[0][1][1]=7

And here’s how you loop through all matches

$start = array();
$end = array();
foreach($matches[0] as $match) {
    $start[] = $match[1];
    $end[] = $match[1] + strlen($match[0]);
}