Custom C++ cout class - output to both console and log file

Question

I'm working on a program that makes heavy use of "cout << strSomething;" to log information to the console. I need to modify the program so that all console output goes to both the console AND a file. Although I can modify the "cout <<" in our code, there are several large third party libraries that also use "cout <<"; those libraries cannot be modified due to their licenses - so modifying all references to "cout <<" is not a solution. Also, the use of "wtee.exe" isn't possible due to the manner in which the command lines are executed.

I am using Visual Studio 2008. I've seen the posting at Google Groups: redirect cout to file, which appears to do EXACTLY what I want to do. The only problem is that the code won't compile. I get C2248 errors "cannot access protected member" on the ->overflow() and ->sync() method calls.

Would anyone know how to get this code to compile? Or an alternate way of redirecting cout to both console and file simultaneously?

Answer 1

The boost::iostreams::tee_device is made for this

#include <boost/iostreams/stream.hpp>
#include <boost/iostreams/tee.hpp>

#include <fstream>
#include <iostream>

int
main()
{
    typedef boost::iostreams::tee_device<std::ostream, std::ofstream> Tee;
    typedef boost::iostreams::stream<Tee> TeeStream;

    std::ofstream file( "foo.out" );
    Tee tee( std::cout, file );

    TeeStream both( tee );

    both << "this goes to both std::cout and foo.out" << std::endl;

    return 0;
}

sample invocation:

samm$ ./a.out
this goes to both std::cout and foo.out
samm$ cat foo.out
this goes to both std::cout and foo.out
samm$