How to get file names under a folder in C++

As per my earlier post How to transform between a double date-time and std::string in C++, some things are surprisingly hard in C++, especially compared to writing in a .NET language. I recently tracked down this useful snippet of code on the internet in order to recursively build a list of files matching some file extension under a folder. This only compiles on Windows – if you want something cross-platform, look at boost (I wanted to avoid bringing the boost filesystem library into my project as yet another dependency).

void accumulate_files(
  const std::string& folder,
  const std::string& extension,
  std::vector<std::string>& file_names )
{
  std::ostringstream oss;
  oss << folder << "\\";
  std::string search_path = oss.str();

  WIN32_FIND_DATA fd;
  HANDLE hFind = ::FindFirstFile( search_path.c_str(), &fd );
  if( hFind != INVALID_HANDLE_VALUE)
  {
    do
    {
      std::string file_name = fd.cFileName;
      std::ostringstream full_file_name;
      full_file_name << folder << "\\" << file_name;

      if ( boost::algorithm::ends_with( file_name, extension ) )
      {
        file_names.push_back( file_name );
      }
      else if ( file_name != "." && file_name != ".." && !file_name.empty() )
      {
        // Recursively call into next directory
        accumulate_files( full_file_name.c_str(), extension, file_names );
      }
    }
    while( ::FindNextFile(hFind, &fd) );

    ::FindClose(hFind);
  }
}

For production code, you’d also want to wrap the file handle in a smart pointer to ensure it gets closed properly for exception safety.