Use cout or cerr to output to console after it has been redirected to file

问题

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?

回答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;

回答2:

You save the buffer and restore it later:

std::streambuf *buf = std::cout.rdbuf(); //save
// Do other stuff
std::cout.rdbuf(buf); // restore

来源：https://stackoverflow.com/questions/14287777/use-cout-or-cerr-to-output-to-console-after-it-has-been-redirected-to-file