How to use the result of std::regex_search?

Question

I'm simply calling

std::smatch m;
if (std::regex_search 
  (std::string (strT.GetString ()), 
  m,
  std::regex ("((\\d[\\s_\\-.]*){10,13})")))
{
  ...
}

I can't for the life of me figure out how to extract the matched values from m.

EVERY SINGLE page on the subject writes it to cout which is worthless to me. I just want to get what's been captured in a string, but no matter what I try it crashes with a "string iterators incompatible" error message.

OK so I tried a few more things and got annoyed at a lot more, most notably about how the same code worked in online testers but not on my computer. I've come down to this

std::string s (strT.GetString ()) ;
std::smatch m;
if (std::regex_search (
    s, 
    m,
    std::regex ("((\\d[\\s_\\-.]*){10,13})")))
{
    std::string v = m[ 0 ] ;
}

working, but this

std::smatch m;
if (std::regex_search (
    std::string (strT.GetString ()), 
    m,
    std::regex ("((\\d[\\s_\\-.]*){10,13})")))
{
    std::string v = m[ 0 ] ;
}

Not Working For Some Reason (with the incompatible string iterator error thingy). There's surely some trick to it. I'll let someone who knows explain it.

do you just want to know if string matches the regex or do you want to search items using a regex? — OznOg, May 29 '19 at 18:15
Use `sregex_token_iterator` or `sregex_iterator`. Fix your regex, too, but that is not the current issue. — Wiktor Stribiżew, May 29 '19 at 18:19
My pattern captures exactly what I need, thank you very much. What I don't get is how I can 'read' my captures in the `std::smatch m;` var. — , May 31 '19 at 08:39
@LightnessRacesinOrbit Seems likely. Can you write it in an answer so I'll accept it? Also would it work by placing a `GetBuffer()` instead of the `GetString()` ? While I can see the necessity I don't like using an entire variable for a single line. — , May 31 '19 at 15:24
Yeah I've decided that wasn't a useful dupe. Re-opened and answered. — Lightness Races in Orbit, May 31 '19 at 15:45

score 0 · Accepted Answer · answered May 31 '19 at 15:44

You are correct that you can just assign the match to a std::string; you don't have to use the stream insertion feature.

However, your third example crashes because std::smatch holds references/handles to positions in the original source data … which in your crashy case is the temporary strT.GetString() that went out of scope as soon as the regex was done (read here).

Your second example is correct.

I concede that the C++ regex implementation is not entirely intuitive at first glance.

How to use the result of std::regex_search?

1 Answers1