Question

I don’t know if it is possible to do this. I would like to store the output of various parts of a program in way that I load saved data and display it exactly how it was printed out in the first place.

I know this is probable simple to do in a way, but I’m just wondering if there is a very easy way to make this happen, and to add to an existing program. It would be nice if I could just specify a region of code in which all the output which is printed to the screen is also inserted into a text file, and saved. Is there a boost library I should look at?

Answer 1

You can create a stream buffer which writes to multiple other streams and install it into std::cout. Essentially, this looks something like this:

#include <streambuf>
struct teebuf:
    std::streambuf
{
    teebuf(std::streambuf* sb0, std::streambuf* sb1): sb0_(sb0), sb1_(sb1) {}
    int_type overflow(int_type c) {
        this->sb0_->sputc(c);
        this->sb1_->sputc(c);
        return traits_type::not_eof(c);
    }
    int sync() {
         this->sb0_->pubsync();
         this->sb1_->pubsync();
         return 0;
    }
    std::streambuf* sb0_;
    std::streambuf* sb1_;
};

#include <iostream>
#include <fstream>
int main() {
    std::ofstream   file("file.log");
    teebuf          tee(std::cout.rdbuf(), file.rdbuf());
    std::streambuf* orig(std::cout.rdbuf());
    std::cout.rdbuf(&tee);
    std::cout << "hello, world!\n";
    std::cout.rdbuf(orig);
}

For more details on how this works you can have a look at articles I wrote on exactly this in comp.lang.c++ and comp.lang.c++.moderated (there were multiple articles, more than a decade old…).