Considering the C++ program below, what should be inserted in place of //***** to ensure a 100% clean shutdown?

Question

This is an exam question:

Considering the C++ program below, what should be inserted in place of //***** to ensure a 100% clean shutdown?

#include <iostream>
#include <fstream>

int main(int argc, char* argv[])
{
    using namespace std;

    fstream log("log.txt", ios::out);
    streambuf* clog_buf = clog.rdbuf(log.rdbuf());

    clog << "Test the logger" << endl;

    //*****
}

• A. Nothing is missing.
• B. exit();
• C. clog.rdbuf(clog_buf);
• D. clog.rdbuf(0);
• E. log.rdbuf(0);

I am rather confused on the use of log and clog in this code. Why can't we just create a file and write down everything we need? Any explanation would be appreciated.

Answer 1

clog_buf points to the stream buffer that clog pointed to before you reset it with rdbuf. A clean shutdown can be achieved by resetting clog's stream buffer to what it was before by using C ( clog.rdbuf( clog_buf ); ).

Answer 2

The code is swapping the standard clog stream (which initially works on STDERR) for a file stream. It means that any code anywhere in the program that streams to clog will actually now stream to a file instead. It's a good localised way to redirect log output, which doesn't require search/replacing ten million utterances of the text clog in your source code.

The answer is C, which reverts the clog stream back to the way you found it before the implicit return 0 kicks in and the program ends gracefully, including the normal file stream destruction.

exit() is a non-graceful shutdown which would not close your file stream properly.

Answer 3

This code does not appear to be exception safe. Therefore, in the face of exceptions, none of the answers will ensure a 100% clean shutdown.