c++ - Do I need to manually close an ifstream?

Question

Do I need to manually call close() when I use a std::ifstream?

For example, in the code:

std::string readContentsOfFile(std::string fileName) {

  std::ifstream file(fileName.c_str());

  if (file.good()) {
      std::stringstream buffer;
      buffer << file.rdbuf();
      file.close();

      return buffer.str();
  }
  throw std::runtime_exception("file not found");
}

Do I need to call file.close() manually? Shouldn't ifstream make use of RAII for closing files?

Answer 1

NO

This is what RAII is for, let the destructor do its job. There is no harm in closing it manually, but it's not the C++ way, it's programming in C with classes.

If you want to close the file before the end of a function you can always use a nested scope.

In the standard (27.8.1.5 Class template basic_ifstream), ifstream is to be implemented with a basic_filebuf member holding the actual file handle. It is held as a member so that when an ifstream object destructs, it also calls the destructor on basic_filebuf. And from the standard (27.8.1.2), that destructor closes the file:

virtual ?basic_filebuf();

Effects: Destroys an object of class basic_filebuf<charT,traits>. Calls close().