dave@superelite.net wrote:
Hi, im having trouble with a base case for regex_search and the number of hits it finds in a haystack. I am wondering if i am not setting flags that need to be set, but i cannot find anything for this in the docs. My usage only seems to find the string "HELLO" once, as the cout indicates xcmMatch.size() is 1 after i run this. I am using boost libs 1.31.00 . Thanks!
You're misunderstanding what match_results contains and what regex_search does: regex_search finds the *first* possible match *only*, the match_results structure contains that match plus any marked sub-expressions, so had your expression been "(HEL)(LOW)" then match_result::size() would have returned 3: item 0 would have been "HELLO", item 1 "HEL", and item 2 "LOW". If you want to find all the matches in a string then you have to iterate through them: try regex_iterator or if you just want the string and don't care about sub-expression matches then regex_token_iterator will also do what you want. Finally I note in your code that you're calling c_str() on the strings and then passing that to the algorithms: that's inefficient, the first thing that the algorithm has to do then is determine how long the string is, but hold on, std::string already knows that! Pass the string to the algorithm instead, it won't make much difference for short strings, but if you have a lot of longish strings to match it makes a huge difference. John.