Should You Manually Close an `ifstream` in C ?

Does Closing an ifstream Manually Enhance RAII?

Question:

When utilizing std::ifstream, should we manually invoke close()? Isn't RAII employed by ifstream to automatically handle file closures?

Example 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");
}

Is calling file.close() necessary? Doesn't ifstream employ RAII for file closure?

Answer:

No.

RAII is designed precisely for this purpose. Allow the destructor to perform its intended function. Manually closing the file does not cause any harm, but it deviates from C conventions and resembles programming in C with classes.

If you need to close the file before a function's end, you can employ nested scopes:

std::ifstream file(fileName.c_str());
{
    std::stringstream buffer;
    buffer << file.rdbuf();
} // scope ends; file closed here

According to the standard (27.8.1.5, Class template basic_ifstream), ifstream should be implemented with a basic_filebuf member that houses the genuine file handle. This member ensures that when an ifstream object gets destroyed, it also calls the basic_filebuf destructor. And as per the standard (27.8.1.2), this destructor closes the file:

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

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