How to override cout in C++?

Question

I have a requirement, I need to use printf and cout to display the data into console and file as well. For printf I have

Answer 1

You can swap the underlying buffers. Here is that done facilitated through RAII.

#include 

class buffer_restore
{
    std::ostream&   os;
    std::streambuf* buf;
public:
    buffer_restore(std::ostream& os) : os(os), buf(os.rdbuf())
    { }

    ~buffer_restore()
    {
        os.rdbuf(buf);
    }
};

int main()
{
    buffer_restore b(std::cout);
    std::ofstream file("file.txt");

    std::cout.rdbuf(file.rdbuf());
    // ...
}