C++ regex error

Question

I've been playing with regex in C++ but ran into some errors:

Here is my script

#include <iostream>
#include <regex>
using namespace std;

string input(string prompt)
{
    cout << prompt;
    string str;
    cin >> str;
    return str;
}

int main() {
    string str;
    while (true) {

        str = input("Enter some text: ");
        regex e("([:w:])+", regex_constants::icase);

        bool match = regex_match(str, e);

        cout << (match? "Matched" : "Not matched") << endl;
    }
}

And when I compile it and run (g++ -std=c++11 test.cpp && ./a.out), I get the following error:

Enter some text: abcde
terminate called after throwing an instance of 'std::regex_error'
  what():  regex_error
Aborted (core dumped)

What's causing it? And is there a way to fix it?

GCC version: gcc version 4.7.2 20121109 (Red Hat 4.7.2-8) (GCC)

OK. I tried boost.regex (with no luck). You can find the file here: http://www.mitchr.me/SS/exampleCode/boost/regexExample1.cpp.html

And here is the output from g++ test.cpp && ./a.out:

/tmp/ccq38Rqf.o: In function `char boost::re_detail::global_lower<char>(char)':
test.cpp:(.text._ZN5boost9re_detail12global_lowerIcEET_S2_[_ZN5boost9re_detail12global_lowerIcEET_S2_]+0x14): undefined reference to `boost::re_detail::do_global_lower(char)'
/tmp/ccq38Rqf.o: In function `char boost::re_detail::global_upper<char>(char)':
test.cpp:(.text._ZN5boost9re_detail12global_upperIcEET_S2_[_ZN5boost9re_detail12global_upperIcEET_S2_]+0x14): undefined reference to `boost::re_detail::do_global_upper(char)'
/tmp/ccq38Rqf.o: In function `bool boost::regex_match<char const*, std::allocator<boost::sub_match<char const*> >, char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >(char const*, char const*, boost::match_results<char const*, std::allocator<boost::sub_match<char const*> > >&, boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > > const&, boost::regex_constants::_match_flags)':
test.cpp:(.text._ZN5boost11regex_matchIPKcSaINS_9sub_matchIS2_EEEcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEEbT_SA_RNS_13match_resultsISA_T0_EERKNS_11basic_regexIT1_T2_EENS_15regex_constants12_match_flagsE[_ZN5boost11regex_matchIPKcSaINS_9sub_matchIS2_EEEcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEEbT_SA_RNS_13match_resultsISA_T0_EERKNS_11basic_regexIT1_T2_EENS_15regex_constants12_match_flagsE]+0x77): undefined reference to `boost::re_detail::perl_matcher<char const*, std::allocator<boost::sub_match<char const*> >, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::match()'
/tmp/ccq38Rqf.o: In function `boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::assign(char const*, char const*, unsigned int)':
test.cpp:(.text._ZN5boost11basic_regexIcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEE6assignEPKcS7_j[_ZN5boost11basic_regexIcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEE6assignEPKcS7_j]+0x2a): undefined reference to `boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::do_assign(char const*, char const*, unsigned int)'
/tmp/ccq38Rqf.o: In function `boost::re_detail::perl_matcher<char const*, std::allocator<boost::sub_match<char const*> >, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::perl_matcher(char const*, char const*, boost::match_results<char const*, std::allocator<boost::sub_match<char const*> > >&, boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > > const&, boost::regex_constants::_match_flags, char const*)':
test.cpp:(.text._ZN5boost9re_detail12perl_matcherIPKcSaINS_9sub_matchIS3_EEENS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEC2ES3_S3_RNS_13match_resultsIS3_S6_EERKNS_11basic_regexIcSA_EENS_15regex_constants12_match_flagsES3_[_ZN5boost9re_detail12perl_matcherIPKcSaINS_9sub_matchIS3_EEENS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEC5ES3_S3_RNS_13match_resultsIS3_S6_EERKNS_11basic_regexIcSA_EENS_15regex_constants12_match_flagsES3_]+0xf6): undefined reference to `boost::re_detail::perl_matcher<char const*, std::allocator<boost::sub_match<char const*> >, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::construct_init(boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > > const&, boost::regex_constants::_match_flags)'
/tmp/ccq38Rqf.o: In function `bool boost::regex_search<char const*, std::allocator<boost::sub_match<char const*> >, char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >(char const*, char const*, boost::match_results<char const*, std::allocator<boost::sub_match<char const*> > >&, boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > > const&, boost::regex_constants::_match_flags, char const*)':
test.cpp:(.text._ZN5boost12regex_searchIPKcSaINS_9sub_matchIS2_EEEcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEEbT_SA_RNS_13match_resultsISA_T0_EERKNS_11basic_regexIT1_T2_EENS_15regex_constants12_match_flagsESA_[_ZN5boost12regex_searchIPKcSaINS_9sub_matchIS2_EEEcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEEbT_SA_RNS_13match_resultsISA_T0_EERKNS_11basic_regexIT1_T2_EENS_15regex_constants12_match_flagsESA_]+0xa2): undefined reference to `boost::re_detail::perl_matcher<char const*, std::allocator<boost::sub_match<char const*> >, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::find()'
/tmp/ccq38Rqf.o: In function `bool boost::regex_search<__gnu_cxx::__normal_iterator<char const*, std::string>, std::allocator<boost::sub_match<__gnu_cxx::__normal_iterator<char const*, std::string> > >, char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >(__gnu_cxx::__normal_iterator<char const*, std::string>, __gnu_cxx::__normal_iterator<char const*, std::string>, boost::match_results<__gnu_cxx::__normal_iterator<char const*, std::string>, std::allocator<boost::sub_match<__gnu_cxx::__normal_iterator<char const*, std::string> > > >&, boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > > const&, boost::regex_constants::_match_flags, __gnu_cxx::__normal_iterator<char const*, std::string>)':
test.cpp:(.text._ZN5boost12regex_searchIN9__gnu_cxx17__normal_iteratorIPKcSsEESaINS_9sub_matchIS5_EEEcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEEbT_SD_RNS_13match_resultsISD_T0_EERKNS_11basic_regexIT1_T2_EENS_15regex_constants12_match_flagsESD_[_ZN5boost12regex_searchIN9__gnu_cxx17__normal_iteratorIPKcSsEESaINS_9sub_matchIS5_EEEcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEEbT_SD_RNS_13match_resultsISD_T0_EERKNS_11basic_regexIT1_T2_EENS_15regex_constants12_match_flagsESD_]+0xa2): undefined reference to `boost::re_detail::perl_matcher<__gnu_cxx::__normal_iterator<char const*, std::string>, std::allocator<boost::sub_match<__gnu_cxx::__normal_iterator<char const*, std::string> > >, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::find()'
/tmp/ccq38Rqf.o: In function `boost::re_detail::perl_matcher<__gnu_cxx::__normal_iterator<char const*, std::string>, std::allocator<boost::sub_match<__gnu_cxx::__normal_iterator<char const*, std::string> > >, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::perl_matcher(__gnu_cxx::__normal_iterator<char const*, std::string>, __gnu_cxx::__normal_iterator<char const*, std::string>, boost::match_results<__gnu_cxx::__normal_iterator<char const*, std::string>, std::allocator<boost::sub_match<__gnu_cxx::__normal_iterator<char const*, std::string> > > >&, boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > > const&, boost::regex_constants::_match_flags, __gnu_cxx::__normal_iterator<char const*, std::string>)':
test.cpp:(.text._ZN5boost9re_detail12perl_matcherIN9__gnu_cxx17__normal_iteratorIPKcSsEESaINS_9sub_matchIS6_EEENS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEC2ES6_S6_RNS_13match_resultsIS6_S9_EERKNS_11basic_regexIcSD_EENS_15regex_constants12_match_flagsES6_[_ZN5boost9re_detail12perl_matcherIN9__gnu_cxx17__normal_iteratorIPKcSsEESaINS_9sub_matchIS6_EEENS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEC5ES6_S6_RNS_13match_resultsIS6_S9_EERKNS_11basic_regexIcSD_EENS_15regex_constants12_match_flagsES6_]+0x116): undefined reference to `boost::re_detail::perl_matcher<__gnu_cxx::__normal_iterator<char const*, std::string>, std::allocator<boost::sub_match<__gnu_cxx::__normal_iterator<char const*, std::string> > >, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::construct_init(boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > > const&, boost::regex_constants::_match_flags)'
/tmp/ccq38Rqf.o: In function `boost::re_detail::basic_regex_formatter<boost::re_detail::string_out_iterator<std::string>, boost::match_results<__gnu_cxx::__normal_iterator<char const*, std::string>, std::allocator<boost::sub_match<__gnu_cxx::__normal_iterator<char const*, std::string> > > >, boost::regex_traits_wrapper<boost::regex_traits<char, boost::cpp_regex_traits<char> > >, char const*>::toi(char const*&, char const*, int, mpl_::bool_<true> const&)':
test.cpp:(.text._ZN5boost9re_detail21basic_regex_formatterINS0_19string_out_iteratorISsEENS_13match_resultsIN9__gnu_cxx17__normal_iteratorIPKcSsEESaINS_9sub_matchIS9_EEEEENS_20regex_traits_wrapperINS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEES8_E3toiERS8_S8_iRKN4mpl_5bool_ILb1EEE[_ZN5boost9re_detail21basic_regex_formatterINS0_19string_out_iteratorISsEENS_13match_resultsIN9__gnu_cxx17__normal_iteratorIPKcSsEESaINS_9sub_matchIS9_EEEEENS_20regex_traits_wrapperINS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEEES8_E3toiERS8_S8_iRKN4mpl_5bool_ILb1EEE]+0x31): undefined reference to `boost::cpp_regex_traits<char>::toi(char const*&, char const*, int) const'
collect2: error: ld returned 1 exit status

The cause is GCC's "implementation" of regular expressions, which is mostly not there. You won't learn anything useful from it. — Pete Becker, Dec 17 '13 at 17:05
@Cubbi - I'm constantly amazed at how GCC gets a pass on this. If Microsoft had shipped crap like that the comments would be much less forgiving. — Pete Becker, Dec 17 '13 at 17:07
@Pete Jonathan Wakely has an [explaination](http://stackoverflow.com/questions/12530406/is-gcc4-7-buggy-about-regular-expressions/12665408#12665408) of what happened. I do agree with you but I can also see how it's easier to forgive when something you receive for free doesn't quite do what you want, as opposed to something that you've paid for :) — Praetorian, Dec 17 '13 at 17:13
@Praetorian - it doesn't matter how it happened. They intentionally shipped crap. — Pete Becker, Dec 17 '13 at 17:18

score 6 · Accepted Answer · answered Dec 17 '13 at 17:09

6

<regex> was not implemented in GCC (although some of its functions would compile without warnings) until just a few months ago: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53631#c17

To experiment with TR1/C++11 regular expressions, you need to use boost.regex, gcc 4.9, or another standard library implementation (e.g. libc++)

answered Dec 17 '13 at 17:09

Cubbi

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Cubbi, check out my modified answer. I posted output from boost.regex test – JadedTuna Dec 17 '13 at 17:20
@Vik2015 Did you link it properly? – Dec 17 '13 at 17:21
@Vik2015 boost.regex is not a header-only library. `-lboost_regex` – Cubbi Dec 17 '13 at 17:21
@Cubbi, `cannot find -lboost_regex` – JadedTuna Dec 17 '13 at 17:23
@Vik2015 You need to point to the boost lib directory, something like `-L/usr/share/boost/lib` – Dec 17 '13 at 17:23
Nevermind. Just read that I have to install boost-devel to make it work. Now it runs perfectly :) – JadedTuna Dec 17 '13 at 17:30

C++ regex error

1 Answers1