Is there a way to create a common output stream object to print on the console and to a file in c++?

Question

I am writing a code where I have to print the same data on the console and to a file. Is there a way to populate a common output stream object and then display it on console using cout and export it to a file, using fstream and iostream libraries?

Answer 1

Sure. You'd just create a suitable stream buffer which probably stores to other stream buffers it writes to internally. Using this stream buffer you'd then create an std::ostream you are writing to.

For example, here is a simple implementation of this approach:

#include <streambuf>
#include <ostream>

class teebuf
    : public std::streambuf
{
    std::streambuf* sb1_;
    std::streambuf* sb2_;

    int overflow(int c) {
        typedef std::streambuf::traits_type traits;
        bool rc(true);
        if (!traits::eq_int_type(traits::eof(), c)) {
            traits::eq_int_type(this->sb1_->sputc(c), traits::eof())
                && (rc = false);
            traits::eq_int_type(this->sb2_->sputc(c), traits::eof())
                && (rc = false);
        }
        return rc? traits::not_eof(c): traits::eof();
    }
    int sync() {
        bool rc(false);
        this->sb1_->pubsync() != -1 || (rc = false);
        this->sb2_->pubsync() != -1 || (rc = false);
        return rc? -1: 0;
    }
public:
    teebuf(std::streambuf* sb1, std::streambuf* sb2)
        : sb1_(sb1), sb2_(sb2) {
    }
};

class oteestream
    : private virtual teebuf
    , public std::ostream {
public:
    oteestream(std::ostream& out1, std::ostream& out2)
        : teebuf(out1.rdbuf(), out2.rdbuf())
        , std::ostream(this) {
        this->init(this);
    }
};

#include <fstream>
#include <iostream>

int main()
{
    std::ofstream fout("tee.txt");
    oteestream    tee(fout, std::cout);
    tee << "hello, world!\n";
}