Javascript lastIndex regex property to PHP regex - php

Question

I'm trying to translate a javascript script in PHP. So far is going good, but I stumbled across some code on which I'm clueless:
while (match = someRegex.exec(text)) {
m = match[0];
if (m === "-") {
var lastIndex = someRegex.lastIndex,
nextToken = someRegex.exec(parts.content);
if (nextToken) {
...
}
someRegex.lastIndex = lastIndex;
}
}
The someRegex variable looks like this:
/[^\\-]+|-|\\(?:[0-3][0-7]{0,2}|[4-7][0-7]?|x[0-9A-Fa-f]{2}|u[0-9A-Fa-f]{4}|c[A-Za-z]|[\S\s]?)/g
exec should be equivalent to preg_match_all in PHP:
preg_match_all($someRegex, $text, $match);
$match = $match[0]; // I get the same results so it works
foreach($match as $m){
if($m === '-'){
// here I don't know how to handle lastIndex and the 2nd exec :(
}
}

Answer 1

I wouldn't use that lastIndex magic at all - essentially you're executing the regex twice on each index. If you really want to do that, you'd need to set the PREG_OFFSET_CAPTURE flag in preg_match_all so that you can get the position, add capture length and use it as the next preg_match offset.
Better use something like this:
preg_match_all($someRegex, $text, $match);
$match = $match[0]; // get all matches (no groups)
$len = count($match);
foreach($match as $i=>$m){
if ($m === '-') {
if ($i+1 < $len) {
$nextToken = $match[$i+1];
…
}
…
}
…
}

Answer 2

Actually, exec is not equivalent to preg_match_all, as exec stops at the first match (the g modifier only sets the lastIndex value to loop through the string). It's equivalent to preg_match.
So you find the first match, get the value thanks to the $array argument, the offset of this value (contained in $flags) and continue your search by setting the offset (last argument).
I guess the second execution won't be a problem as you'll do exactly the same thing as in the javascript version.
Note that I haven't tried the loop, but it should be pretty straightforward once you've figured out how preg_match works exactly with the optional arguments (I'll run some test).
$lastIndex = 0;
while(preg_match($someRegex, $text, $match, PREG_OFFSET_CAPTURE, $lastIndex) {
$m = $match[0][0];
$lastIndex = $match[0][1] + strlen($m); //thanks Bergi for the correction
if($m === '-') {
// assuming the $otherText relate to the parts.content thing
if(preg_match($someRegex, $otherText, $secondMatch, 0, $lastIndex)) {
$nextToken = $secondMatch[0];
...
}
}
}
I guess that should be it (excuse any small error, haven't done php for a while).