dlib C++ Library - logger_custom_output_ex.cpp

    // The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt

    /*

        This is an example showing how to control where the dlib::logger sends its messages.
        This is done by creating a "hook" class that is called whenever any of the loggers want
        to log a message.  The hook class then outputs the messages using any method you like.

        Prior to reading this example, you should understand the basics of the dlib::logger.
        So you should have already read the logger_ex.cpp and logger_ex_2.cpp example programs.

    */

    #include <dlib/logger.h>

    using namespace dlib;
    using namespace std;

    class my_hook
    {
    public:
        my_hook(
        )
        {
            fout.open("my_log_file.txt");
        }

        void log (
            const string& logger_name,
            const log_level& ll,
            const uint64 thread_id,
            const char* message_to_log
        )
        {
            // Log all messages from any logger to our log file.
            fout << ll << " ["<<thread_id<<"] " << logger_name << ": " << message_to_log << endl;

            // But only log messages that are of LINFO priority or higher to the console.
            if (ll >= LINFO)
                cout << ll << " ["<<thread_id<<"] " << logger_name << ": " << message_to_log << endl;
        }

    private:
        ofstream fout;
    };

    int main()
    {
        my_hook hook;
        // This tells all dlib loggers to send their logging events to the hook object.  That
        // is, any time a logger generates a message it will call hook.log() with the message
        // contents.  Additionally, hook.log() will also only be called from one thread at a
        // time so it is safe to use this kind of hook in a multi-threaded program with many
        // loggers in many threads.
        set_all_logging_output_hooks(hook);
        // It should also be noted that the hook object must not be destructed while the
        // loggers are still in use.  So it is a good idea to declare the hook object
        // somewhere where it will live the entire lifetime of the program, as we do here.

        logger dlog("main");
        // Tell the dlog logger to emit a message for all logging events rather than its
        // default behavior of only logging LERROR or above.
        dlog.set_level(LALL);

        // All these message go to my_log_file.txt, but only the last two go to the console.
        dlog << LDEBUG << "This is a debugging message.";
        dlog << LINFO  << "This is an informational message.";
        dlog << LERROR << "An error message!";
    }