When will ofstream::open fail?

Question

I am trying out try, catch, throw statements in C++ for file handling, and I have written a dummy code to catch all errors. My question is in order to check if I have got th

Answer 1

To get ofstream::open to fail, you need to arrange for it to be impossible to create the named file. The easiest way to do this is to create a directory of the exact same name before running the program. Here's a nearly-complete demo program; arranging to reliably remove the test directory if and only if you created it, I leave as an exercise.

#include 
#include 
#include 
#include 
#include 

using std::ofstream;
using std::strerror;
using std::cerr;

int main() 
{
    ofstream outfile;

    // set up conditions so outfile.open will fail:
    if (mkdir("test.txt", 0700)) {
        cerr << "mkdir failed: " << strerror(errno) << '\n';
        return 2;
    }

    outfile.open("test.txt");
    if (outfile.fail()) {
        cerr << "open failure as expected: " << strerror(errno) << '\n';
        return 0;
    } else {
        cerr << "open success, not as expected\n";
        return 1;
    }
}

There is no good way to ensure that writing to an fstream fails. I would probably create a mock ostream that failed writes, if I needed to test that.