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!";
}