Do I need to manually close a 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?

I've searched through most of the questions here and none were addressing this.

Thanks

Answer 1

The best practice is to close it once you are done with it.

Answer 2

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, that destructor closes the file:

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

Answer 3

Do you need to close the file?
NO

Should you close the file?
Depends.

Do you care about the possible error conditions that could occur if the file fails to close correctly? Remember that close calls setstate(failbit) if it fails. The destructor will call close() for you automatically because of RIAA but will not leave you a way of testing the fail bit as the object no longer exists.

Answer 4

No, this is done automatically by the constructor. The only reason you should call it manually, is because the fstream instance has a big scope, for example if it is a member variable of a long living class instance.