如何组合输出流，以便输出一次到达多个位置?

I was thinking of doing something like this:

class stream_compose : public streambuf, private boost::noncopyable
{
public:
    // take two streams, save them in stream_holder,
    // this set their buffers to `this`.
    stream_compose;

    // implement the streambuf interface, routing to both
    // ...

private:
    // saves the streambuf of an ios class,
    // upon destruction restores it, provides
    // accessor to saved stream
    class stream_holder;

    stream_holder mStreamA;
    stream_holder mStreamB;
};

这似乎很直接.然后 main 中的调用将类似于:

// anything that goes to cout goes to both cout and the file
stream_compose coutToFile(std::cout, theFile);
// and so on