simple CPP regex examples

regex_example.cpp

#include <iostream>
#include <regex>
#include <sstream>

int main()
{
  std::string str = "[A,B,15] [C,D,1] [C,D,2][G,H,9] [C,D,a] [C,D,9] [E,F,00177] ";
  std::regex word_regex( "\\[([A-Z]),([A-Z]),(\\d+)\\]" );

  // get words and check if each of them matches the regex
  {
    std::istringstream iss( str );
    while ( iss.good() )
    {
      std::string word;
      iss >> word;

      std::smatch match;
      if ( std::regex_match( word, match, word_regex ) )
      {
        int length = 0;
        std::istringstream decimal_ss( match[3] );
        decimal_ss >> length;

        std::cout << "from : " << match[1] << ", to : " << match[2] << ", length : " << length << std::endl;
      }
      else
      {
        std::cout << "\"" << word << "\" does not match." << std::endl;
      }
    }
  }

  //  outputs
  //
  //  from : A, to : B, length : 15
  //  from : C, to : D, length : 1
  //  "[C,D,2][G,H,9]" does not match.
  //  "[C,D,a]" does not match.
  //  from : C, to : D, length : 9
  //  from : E, to : F, length : 177
  //  "" does not match.

  // prints all matched parts
  {
    for ( auto it = std::sregex_iterator( str.begin(), str.end(), word_regex ); it != std::sregex_iterator(); ++it )
    {
      const auto& elem = *it;
      std::cout << "from : " << elem[1] << ", to : " << elem[2] << ", length : " << std::stoi( elem[3] ) << std::endl;
    }
  }

  // outputs
  //
  //  from : A, to : B, length : 15
  //  from : C, to : D, length : 1
  //  from : C, to : D, length : 2
  //  from : G, to : H, length : 9
  //  from : C, to : D, length : 9
  //  from : E, to : F, length : 177

  return 0;
}