How to control level of debugging info in glib? - c

Question

I have a library written in C with glib/gobject. It produces significant number of debugging information via g_debug() call. This info is very helpful for troubleshooting, however I do not want it to be shown, when library is included with actual application. So, basically I need a way to control/filter amount of debugging information and I could not figure out how it supposed to work with glib. Could someone point me in the right direction, please?

Answer 1

You could try setting G_DEBUG environment variable as mentioned in the GLib developer site. Please refer to Environment variable section under Running and debugging GLib Applications in http://developer.gnome.org/glib/2.28/glib-running.html.
EDIT: Update to set the logger in the code.
You can use g_log_set_handler ( http://developer.gnome.org/glib/2.29/glib-Message-Logging.html#g-log-set-handler ) to do this in your code. Initially you can set the log handler to a dummy function which display nothings & then you can set the log handler to g_log_default_handler based on the argument passed for set appropriate log levels. To set the log levels above a set level you will need to manipulate GLogLevelFlags values as per your need.
Hope the below code sample will provide some pointers
#include <glib.h>
#include <stdio.h>
#include <string.h>
#define G_LOG_DOMAIN ((gchar*) 0)
static void _dummy(const gchar *log_domain,
GLogLevelFlags log_level,
const gchar *message,
gpointer user_data )
{
/* Dummy does nothing */
return ;
}
int main(int argc, char **argv)
{
/* Set dummy for all levels */
g_log_set_handler(G_LOG_DOMAIN, G_LOG_LEVEL_MASK, _dummy, NULL);
/* Set default handler based on argument for appropriate log level */
if ( argc > 1)
{
/* If -vv passed set to ONLY debug */
if(!strncmp("-vv", argv[1], 3))
{
g_log_set_handler(G_LOG_DOMAIN, G_LOG_LEVEL_DEBUG, g_log_default_handler, NULL);
}
/* If -v passed set to ONLY info */
else if(!strncmp("-v", argv[1], 2))
{
g_log_set_handler(G_LOG_DOMAIN, G_LOG_LEVEL_INFO, g_log_default_handler, NULL);
}
/* For everything else, set to back to default*/
else
{
g_log_set_handler(G_LOG_DOMAIN, G_LOG_LEVEL_MASK, g_log_default_handler, NULL);
}
}
else /* If no arguments then set to ONLY warning & critical levels */
{
g_log_set_handler(G_LOG_DOMAIN, G_LOG_LEVEL_WARNING| G_LOG_LEVEL_CRITICAL, g_log_default_handler, NULL);
}
g_warning("This is warning\n");
g_message("This is message\n");
g_debug("This is debug\n");
g_critical("This is critical\n");
g_log(NULL, G_LOG_LEVEL_INFO , "This is info\n");
return 0;
}
Hope this helps!

Answer 2

I implemented custom log handler and here is how it turned out:
void custom_log_handler (const gchar *log_domain, GLogLevelFlags log_level, const gchar *message, gpointer user_data)
{
gint debug_level = GPOINTER_TO_INT (user_data);
/* filter out messages depending on debugging level */
if ((log_level & G_LOG_LEVEL_DEBUG) && debug_level < MyLogLevel_DEBUG) {
return;
}
else if ((log_level & G_LOG_LEVEL_INFO) && debug_level < MyLogLevel_INFO) {
return;
}
g_printf ("%s\n", message);
}
int main(int argc, char *argv[])
{
...
if (verbose) {
g_log_set_handler (NULL, G_LOG_LEVEL_MASK, custom_log_handler, GINT_TO_POINTER (MyLogLevel_DEBUG));
}
else {
g_log_set_handler (NULL, G_LOG_LEVEL_MASK, custom_log_handler, GINT_TO_POINTER (MyLogLevel_NORMAL));
}
...
}
I hope it will be helpful to somebody :-)

Answer 3

You can control whether to print debug (log) messages with setting the G_MESSAGES_DEBUG environment variable when running your application.
The easiest is to use $ G_MESSAGES_DEBUG=all ./your-app when you need debugging (log) messages to be printed.
However, when G_MESSAGES_DEBUG=all glib libraries itself print debug (log) messages too which you may not need. So, predefine G_LOG_DOMAIN as a separate custom log domain string for your application and set G_MESSAGES_DEBUG to the same string when running. For example, use -DG_LOG_DOMAIN=\"my-app\" among compiler flags and run application with $ G_MESSAGES_DEBUG="my-app" ./your-app.