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?

1
179
11/4/2014 9:19:57 PM

Accepted Answer

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 ╦ťbasic_filebuf();

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

232
5/4/2011 2:14:14 PM

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 RAII but will not leave you a way of testing the fail bit as the object no longer exists.


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