How to use the result of std::regex_search?

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.

Solution

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.