CODEWITHSUNDEEP
c++regexc++11cygwin
BNR
BNR

Reputation: 55

regex fails to match

my pattern seems to match external regex tester but my program fails. what's wrong with my code ? I would appreciate any comments

my code:

std::smatch matches;

s = "y=a^b,z=(y+76),k=(z|p)";

for (int t=0; t<4; t++) { 

  try {
    std::regex  expr ( "((\\w+)=\\((\\w+)([\\|&\\^\\+\\-\\*])(\\w+)\\))" , regex_constants::extended );    // regex::extended|regex_constants::basic 


    std::regex_match(s, matches, expr);

    if ( matches.empty() ) puts ("No Match !");

enter image description here

Upvotes: 2

Views: 1347

Answers (1)

Cubbi
Cubbi

Reputation: 47448

First, GCC did not support <regex> until 4.9, you will have to upgrade or switch to another compiler (clang or MSVC, for example) or use boost.regex.

Second, regex_match attempts to match the entire string, it will fail. You need regex_search or regex_iterator

Third, your regex is not a valid POSIX ERE (at least according to libc++ and gcc 4.9), just drop the regex_constants:

#include <regex>
#include <iostream>
int main()
{
    std::smatch matches;
    std::string s = "y=a^b,z=(y+76),k=(z|p)";
    std::regex  expr(R"((\w+)=\((\w+)([|&^+*-])(\w+)\))"); // simplified a bit

    for(auto it = std::sregex_iterator(s.begin(), s.end(), expr);
             it != std::sregex_iterator();
           ++it)
    {
         std::cout << "Found a match: " << it->str() << "\n";
         std::smatch m = *it;

         std::cout << "prefix=[" << m.prefix() << "]\n";
         for(std::size_t n = 0; n < m.size(); ++n)
                 std::cout << "   m[" << n << "]=[" << m[n] << "]\n";
         std::cout << "suffix=[" << m.suffix() << "]\n";
    }
}

online demo: http://coliru.stacked-crooked.com/a/559d3bca554517c6

Upvotes: 5

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