Question

Any idea why the following code prints “no match“? Something related with the compiler or the version of the library? I compiled with g++ a.cpp.

#include <tr1/regex>
#include <iostream>
#include <string>

using namespace std;

int main()
{
   const std::tr1::regex pattern("(\\w+day)");

   std::string weekend = "Saturday and Sunday";

   std::tr1::smatch result;

   bool match = std::tr1::regex_search(weekend, result, pattern);

   if(match)
   {
      for(size_t i = 1; i < result.size(); ++i)
      {
         std::cout << result[i] << std::endl;
      }
   }else
    std::cout << "no match" << std::endl;

   return 0;
}

Answer 1

Definitely an issue with your compiler. I would recommend (since you’re on Linux and that makes it particularly easy) to simply swap out <tr1/regex> for <boost/regex.hpp>. The namespace also becomes boost:: instead of std::tr1:: but all other syntax is exactly the same and it may solve all your problems.

If you can’t use boost, that’s a whole different story; but as of the past year or so, most people/employers/companies have been much more boost-friendly.

Also note that your test case is flawed. You have a loop, but it’ll only ever print a single value. regex_search returns a value at a time, you need to keep calling it with the new search start index to get all results. If you said the output of the program was nothing (vs “no match”), then I would say the bug was in your code. But the code as it is currently written should return "Saturday" or "".