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Salathe · 12-11-2007, 05:53 PM

Thanks Geert. The two items ?: and ? are not related. When you specify a group such as (abc), that group is returned as part of the matches array -- it captures whatever is inside as a special group. If you use (?:abc) then the group becomes non-capturing, which simply means that the group is not returned with the matches.

For those who like code snippets, here's what happens:

php Code:

preg_match('/t(es)t/', 'test', $matches);
/*
Array
(
    [0] => test
    [1] => es
)
*/

preg_match('/t(?:es)t/', 'test', $matches);
/*
Array
(
    [0] => test
)
*/

In extension to Geert's post above, the U (PCRE_UNGREEDY) modifier can be used at the end of the regex in order to reverse the normal behaviour. By default, patterns are greedy but with the U modifier they will become non-greedy. In this case, if the ? is used (eg. (.*?) it will make the preceeding quantifier greedy. That's probably confusing to deal with at the moment so I just mention it as an aside.

12-11-2007, 05:53 PM	#4 (permalink)
Salathe Moderateur Join Date: Apr 2007 Posts: 1,381 Thanks: 5	Thanks Geert. The two items `?:` and `?` are not related. When you specify a group such as `(abc)`, that group is returned as part of the matches array -- it captures whatever is inside as a special group. If you use `(?:abc)` then the group becomes non-capturing, which simply means that the group is not returned with the matches. For those who like code snippets, here's what happens: php Code: preg_match('/t(es)t/', 'test', $matches); /* Array ( [0] => test [1] => es ) / preg_match('/t(?:es)t/', 'test', $matches); / Array ( [0] => test ) / In extension to Geert's post above, the `U` (PCRE_UNGREEDY) modifier can be used at the end of the regex in order to reverse the normal behaviour. By default, patterns are greedy but with the U modifier they will become non-greedy. In this case, if the `?` is used (eg. `(.?)` it will make the preceeding quantifier greedy. That's probably confusing to deal with at the moment so I just mention it as an aside.