std regex_search to match only current line

Question

I use a various regexes to parse a C source file, line by line. First i read all the content of file in a string:

ifstream file_stream(\"commented.cpp\",ifstream         


        

Answer 1

#include //comment

The code should fail, my logic is with those options to regex_search, the match should fail, because it should search for pattern in the first line:

#include

But instead it searches whole string, and immideatly finds //comment. I need help, to make regex_search match only in current line.

Are you trying to match all // comments in a source code file, or only the first line?

The former can be done like this:

#include 
#include 
#include 

int main()
{
  auto input = std::ifstream{"stream_union.h"};

  for(auto line = std::string{}; getline(input, line); )
  {
    auto submatch = std::smatch{};
    auto pattern = std::regex(R"(//)");
    std::regex_search(line, submatch, pattern);

    auto match = submatch.str(0);
    if(match.empty()) continue;

    std::cout << line << std::endl;
  }
  std::cout << std::endl;

  return EXIT_SUCCESS;
}

And the later can be done like this:

#include 
#include 
#include 

int main()
{
  auto input = std::ifstream{"stream_union.h"};
  auto line = std::string{};
  getline(input, line);

  auto submatch = std::smatch{};
  auto pattern = std::regex(R"(//)");
  std::regex_search(line, submatch, pattern);

  auto match = submatch.str(0);
  if(match.empty()) { return EXIT_FAILURE; }

  std::cout << line << std::endl;

  return EXIT_SUCCESS;
}

If for any reason you're trying to get the position of the match, tellg() will do that for you.