Redirecting STL Standard Output and Error to a Log File

Logger.h

#pragma once
/*
 * Copyright (c) 2007 Onur Cinar.
 * All Rights Reserved
 *
 * Provided under LGPL license.
 */

#include <fstream>
#include <string>

/**
 * Logger.
 *
 * @author  Onur Cinar
 */
class Logger
{
public:
    /**
     * Constructor.
     *
     * @param[in] logFile log file.
     */
    Logger (const std::string& logFile);

    /**
     * Destructor.
     */
    virtual ~Logger ();

private:
    /** Log stream. */
    std::ofstream logOut;

    /** Old cout. */
    std::streambuf* oldCout;

    /** Old cerr. */
    std::streambuf* oldCerr;

    /** Old clog. */
    std::streambuf* oldClog;
};

Logger.cpp

/*
 * Copyright (c) 2007 Onur Cinar.
 * All Rights Reserved
 *
 * Provided under LGPL license.
 */


#include <iostream>

/**
 * Logger.
 *
 * @author  Onur Cinar
 */

Logger::Logger (const std::string& logFile)
: logOut(logFile.c_str(), std::ios::out | std::ios::trunc)
{
    // Save old stream buffers
    oldCout = std::cout.rdbuf();
    oldCerr = std::cerr.rdbuf();
    oldClog = std::cerr.rdbuf();

    // Redirect cout and cerr
    std::cout.rdbuf(logOut.rdbuf());
    std::cerr.rdbuf(logOut.rdbuf());
    std::clog.rdbuf(logOut.rdbuf());
}

Logger::~Logger ()
{
    // Restore old stream buffers
    std::cout.rdbuf(oldCout);
    std::cerr.rdbuf(oldCerr);
    std::clog.rdbuf(oldClog);

    // Close log
    logOut.close();
}

Here is how we can use it:

#include <iostream>
#include <Logger.h>

int main (int argc, char** argv)
{
    Logger logger("log.txt");

    std::out << "Output" << std::endl;

    std::cerr << "Error" << std::endl;

    std::clog << "Log" << std::end;

    return 0;
}