Can you safely close a file that was never opened?

Question

If I have a std::ofstream that may or may not have been opened, is it safe to try to close regardless? In otherwords does close() do anything nasty (throw exception, etc) if !is_open(). For example

std::ofstream out;
if (some_condition)
{
    out.open(path, std::ios::out);
}

After I'm done with the file, can I just say

out.close();

Or should I first check

if (out.is_open())
    out.close();

The only description of std::basic_fstream::close on cppreference is

Closes the associated file.
Effectively calls rdbuf()->close(). If an error occurs during operation, setstate(failbit) is called.

Answer 1

It does exactly what cppreference says it will: the failbit will be set, and you can inspect it with the fail() method. For instance, the following prints "fail\n":

#include <iostream>
#include <fstream>
int main(int argc, char ** argv)
{
        std::ofstream out;
        out.close();
        if (out.fail())
                std::cout << "fail" << std::endl;
        return 0;
}

In terms of interaction with the operating system, there's nothing there to close, but it's otherwise harmless.

Answer 2

From the C++ standard, §27.9.1.4 [filebuf.members], paragraph 6:

basic_filebuf<charT,traits>* close();
   Effects: If is_open() == false, returns a null pointer.…