Re: Regular expression question

Hello Mat,

Thanks for the detailed response! Also, the first error you pointed out 
was just me not paying attention. It was probably hastily copied from a 
pointer initialization someplace else. And thanks for pointing out the 
second thing. Should I just be careful and cast to an unsigned int and 
use %u from now on?

Regards,
Andrei

On 19.08.2012 16:17, Mat Sutcliffe wrote:
> Hi Andrei,
>
> POSIX regex, which csRegExpMatcher uses, does not return multiple 
> matches. It finds the first match in the string and then stops. The 
> array of matches is populated with sub-matches from parenthesized 
> subexpressions in the pattern.
>
> If you replace your pattern "el" with "(el)" you should get an array 
> with one member. If you use the pattern "((e)(l))" you should get 
> three members. But I think that because of a bug in 
> csRegExpMatcher::Match, those three members will correspond to the 
> substrings "el", "el" and "e". To fix the bug, the array of regmatch_t 
> structures passed to regexec should have length regex.re_nsub+1. Then 
> matching the pattern "el" would give one array member, matching "(el)" 
> would give two members, and "((e)(l))" four members. This is a 
> breaking API change, but would make regexes work as intended. As it is 
> currently, you always lose the final subexpression match.
>
> You could implement multiple matches in the way you expected it to 
> work originally, simply by calling Match again with the offset 
> obtained from the previous call to Match.
>
> Another couple of problems I can see in your pasted code:
>
> csRegExpMatcher matcher = csRegExpMatcher("el", true);
> This says to construct two matchers and then copy one into the other. 
> Maybe your compiler optimises this out, maybe not. Cleaner to just do 
> this:
> csRegExpMatcher matcher ("el", true);
>
> printf("Found %d matches!\n", result.GetSize());
> csArray::GetSize returns a size_t, which is an unsigned integer type, 
> but in printf with the %d format specifier you are treating it as a 
> signed integer, with undefined consequences.
> This should be:
> printf("Found %u matches!\n", static_cast<unsigned 
> int>(result.GetSize()));
> csRegExpMatch::startOffset is also a size_t, so the same applies to 
> where you print the offsets a couple lines below.
> Not sure if the cast is strictly necessary, but better to be safe as 
> size_t is not guaranteed to be the same number of bits as an unsigned 
> int. ISO C defines %zu as printf format specifier for size_t, but MSVC 
> ignores this and uses %Iu (uppercase i, lowercase u), so the "proper" 
> way might be to use the preprocessor to select the appropriate 
> specifier, and then you wouldn't need the cast. That preprocessor guff 
> could be a candidate for inclusion in cssysdef.h.
>


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