dlib C++ Library - logger_ex_2.cpp

// The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
/*
 This is a somewhat complex example illustrating the use of the logger object 
 from the dlib C++ Library. It will demonstrate using multiple loggers and threads. 
 The output of this program looks like this:
 0 INFO [0] example: This is an informational message.
 0 WARN [0] example: The variable is bigger than 4! Its value is 8
 0 INFO [0] example: make two threads
 0 WARN [0] example.test_class: warning! someone called warning()!
 0 INFO [0] example: we are going to sleep for half a second.
 0 INFO [1] example.thread: entering our thread
 0 WARN [1] example.test_class: warning! someone called warning()!
 0 INFO [2] example.thread: entering our thread
 0 WARN [2] example.test_class: warning! someone called warning()!
 203 INFO [1] example.thread: exiting our thread
 203 INFO [2] example.thread: exiting our thread
 503 INFO [0] example: we just woke up
 503 INFO [0] example: program ending
*/
#include <dlib/logger.h>
#include <dlib/misc_api.h>
#include <dlib/threads.h>
using namespace dlib;
/*
 Here we create three loggers. Note that it is the case that:
 - logp.is_child_of(logp) == true
 - logt.is_child_of(logp) == true
 - logc.is_child_of(logp) == true
 logp is the child of itself because all loggers are their own children :) But the other
 two are child loggers of logp because their names start with logp.name() + "." which means
 that whenever you set a property on a logger it will also set that same property on all of
 the logger's children.
*/
logger logp("example");
logger logt("example.thread");
logger logc("example.test_class");
class test
{
public:
 test ()
 {
 // this message won't get logged because LINFO is too low
 logc << LINFO << "constructed a test object";
 }
 ~test ()
 {
 // this message won't get logged because LINFO is too low
 logc << LINFO << "destructed a test object";
 }
 void warning ()
 {
 logc << LWARN << "warning! someone called warning()!";
 }
};
void thread (void*)
{
 logt << LINFO << "entering our thread";
 
 test mytest;
 mytest.warning();
 dlib::sleep(200);
 logt << LINFO << "exiting our thread";
}
void setup_loggers (
)
{
 // Create a logger that has the same name as our root logger logp. This isn't very useful in 
 // this example program but if you had loggers defined in other files then you might not have
 // easy access to them when starting up your program and setting log levels. This mechanism
 // allows you to manipulate the properties of any logger so long as you know its name.
 logger temp_log("example");
 // For this example I don't want to log debug messages so I'm setting the logging level of 
 // All our loggers to LINFO. Note that this statement sets all three of our loggers to this
 // logging level because they are all children of temp_log. 
 temp_log.set_level(LINFO);
 // In addition I only want the example.test_class to print LWARN or higher messages so I'm going
 // to set that here too. Note that we set this value after calling temp_log.set_level(). If we 
 // did it the other way around the set_level() call on temp_log would set logc_temp.level() and 
 // logc.level() back to LINFO since temp_log is a parent of logc_temp.
 logger logc_temp("example.test_class");
 logc_temp.set_level(LWARN);
 // Finally, note that you can also configure your loggers from a text config file. 
 // See the documentation for the configure_loggers_from_file() function for details.
}
int main()
{
 setup_loggers();
 // print our first message. It will go to cout because that is the default.
 logp << LINFO << "This is an informational message.";
 int variable = 8;
 // Here is a debug message. It won't print though because its log level is too low (it is below LINFO).
 logp << LDEBUG << "The integer variable is set to " << variable;
 
 if (variable > 4)
 logp << LWARN << "The variable is bigger than 4! Its value is " << variable;
 logp << LINFO << "make two threads";
 create_new_thread(thread,0);
 create_new_thread(thread,0);
 test mytest;
 mytest.warning();
 logp << LINFO << "we are going to sleep for half a second.";
 // sleep for half a second
 dlib::sleep(500);
 logp << LINFO << "we just woke up";
 logp << LINFO << "program ending";
 // It is also worth pointing out that the logger messages are atomic. This means, for example, that
 // in the above log statements that involve a string literal and a variable, no other thread can
 // come in and print a log message in-between the literal string and the variable. This is good
 // because it means your messages don't get corrupted. However, this also means that you shouldn't 
 // make any function calls inside a logging statement if those calls might try to log a message 
 // themselves since the atomic nature of the logger would cause your application to deadlock.
}