Using regex_search from the C++ regex library

Question

The regex_search function isn't quite behaving as expected.

#include <iostream>
#include <regex>
#include <string>

using namespace std;

int main()
{
    string str = "Hello world";
    const regex rx("Hello");
    cout << regex_search(str.begin(), str.end(), rx) << endl;
    return 0;
}

The output is

What's going on?

Remember that C++11 is quite new, and not all compilers support all features yet. Specifically, GCC do not support regex_searchyet. — Some programmer dude
– Some programmer dude, Commented Sep 5, 2012 at 10:57
Thanks for pointing that out. I guess I'll go look at Boost's regex library now. — wenderen
– wenderen, Commented Sep 5, 2012 at 11:01
@wenderen : Be sure to look into Boost.Xpressive rather than Boost.Regex if you want to avoid having to build Boost (Xpressive is header-only unlike Regex). — ildjarn
– ildjarn, Commented Sep 6, 2012 at 0:45
@JoachimPileborg So what is gcc's intention with this oddity? Why then expose the std::regex_search function if it doesn't work (and his example isn't really an edge case)? I'd rather miss this function than use it while it silently just doesn't work. — Christian Rau
– Christian Rau, Commented Sep 6, 2012 at 8:36
@ChristianRau I don't know what the GCC designers think, but I'm guessing it's better to have a complete interface, even if some of the actual functionality behind that interface is missing. — Some programmer dude
– Some programmer dude, Commented Sep 6, 2012 at 8:40

jotik · Accepted Answer · 2016-04-05 13:42:02Z

1

As pointed out in comments to the question, older implementations of the C++ standard libraries did not yet support all features in C++11. Of course, libc++ being an exception because it was originally built specifically for C++11.

According to this bug report support for <regex> in libstdc++ was only implemented for version 4.9 of GCC. You can check the current status on the libstdc++ status page.

One can confirm, that your example works with GCC 4.9 while still failing with GCC 4.8.

answered Apr 5, 2016 at 13:42

jotik

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