Question

Redirecting cout or cerr to a file is easy enough. I can use this to redirect third party output to a file. However, after I have redirected the third party output to a file, how do I then use cout myself to output to the console?

Answer 1

I’m a great fan of RAII, so I once wrote this small helper class. It will redirect the stream until it goes out of scope, at which point it restores the original buffer. Quite handy. 🙂

class StreamRedirector {
public:
    explicit StreamRedirector(std::ios& stream, std::streambuf* newBuf) :
        savedBuf_(stream.rdbuf()), stream_(stream)
    {
        stream_.rdbuf(newBuf);
    }

    ~StreamRedirector() {
        stream_.rdbuf(savedBuf_);
    }

private:
    std::streambuf* savedBuf_;
    std::ios& stream_;
};

Can be used like this:

using namespace std;
cout << "Hello stdout" << endl;
{
    ofstream logFile("log.txt");
    StreamRedirector redirect(cout, logFile.rdbuf());
    cout << "In log file" << endl;
}
cout << "Back to stdout" << endl;