Message Logging

G_LOG_DOMAIN

#define G_LOG_DOMAIN    ((gchar*) 0)

Defines the log domain. For applications, this is typically left as the default NULL (or "") domain. Libraries should define this so that any messages which they log can be differentiated from messages from other libraries and application code. But be careful not to define it in any public header files.

For example, GTK+ uses this in its Makefile.am:

INCLUDES = -DG_LOG_DOMAIN=\"Gtk\"

G_LOG_FATAL_MASK

#define G_LOG_FATAL_MASK        (G_LOG_FLAG_RECURSION | G_LOG_LEVEL_ERROR)

GLib log levels that are considered fatal by default.

G_LOG_LEVEL_USER_SHIFT

#define G_LOG_LEVEL_USER_SHIFT  (8)

Log level shift offset for user defined log levels (0-7 are used by GLib).

GLogFunc ()

void        (*GLogFunc)                     (const gchar *log_domain,
                                             GLogLevelFlags log_level,
                                             const gchar *message,
                                             gpointer user_data);

Specifies the prototype of log handler functions.

enum GLogLevelFlags

typedef enum
{
  /* log flags */
  G_LOG_FLAG_RECURSION          = 1 << 0,
  G_LOG_FLAG_FATAL              = 1 << 1,

  /* GLib log levels */
  G_LOG_LEVEL_ERROR             = 1 << 2,       /* always fatal */
  G_LOG_LEVEL_CRITICAL          = 1 << 3,
  G_LOG_LEVEL_WARNING           = 1 << 4,
  G_LOG_LEVEL_MESSAGE           = 1 << 5,
  G_LOG_LEVEL_INFO              = 1 << 6,
  G_LOG_LEVEL_DEBUG             = 1 << 7,

  G_LOG_LEVEL_MASK              = ~(G_LOG_FLAG_RECURSION | G_LOG_FLAG_FATAL)
} GLogLevelFlags;

Flags specifying the level of log messages.

g_log ()

void        g_log                           (const gchar *log_domain,
                                             GLogLevelFlags log_level,
                                             const gchar *format,
                                             ...);

Logs an error or debugging message. If the log level has been set as fatal, the abort() function is called to terminate the program.

g_logv ()

void        g_logv                          (const gchar *log_domain,
                                             GLogLevelFlags log_level,
                                             const gchar *format,
                                             va_list args);

Logs an error or debugging message. If the log level has been set as fatal, the abort() function is called to terminate the program.

g_message()

#define     g_message(...)

A convenience function/macro to log a normal message.

g_warning()

#define     g_warning(...)

A convenience function/macro to log a warning message.

g_critical()

#define     g_critical(...)

Logs a "critical warning" (G_LOG_LEVEL_CRITICAL). It's more or less application-defined what constitutes a critical vs. a regular warning. You could call g_log_set_always_fatal() to make critical warnings exit the program, then use g_critical() for fatal errors, for example.

g_error()

#define     g_error(...)

A convenience function/macro to log an error message. Error messages are always fatal, resulting in a call to abort() to terminate the application. This function will result in a core dump; don't use it for errors you expect. Using this function indicates a bug in your program, i.e. an assertion failure.

g_log_set_handler ()

guint       g_log_set_handler               (const gchar *log_domain,
                                             GLogLevelFlags log_levels,
                                             GLogFunc log_func,
                                             gpointer user_data);

Sets the log handler for a domain and a set of log levels. To handle fatal and recursive messages the log_levels parameter must be combined with the G_LOG_FLAG_FATAL and G_LOG_FLAG_RECURSIVE bit flags.

Note that since the G_LOG_LEVEL_ERROR log level is always fatal, if you want to set a handler for this log level you must combine it with G_LOG_FLAG_FATAL.

  g_log_set_handler (NULL, G_LOG_LEVEL_WARNING | G_LOG_FLAG_FATAL
                     | G_LOG_FLAG_RECURSIVE, my_log_handler, NULL);

  g_log_set_handler ("Gtk", G_LOG_LEVEL_CRITICAL | G_LOG_FLAG_FATAL
                     | G_LOG_FLAG_RECURSIVE, my_log_handler, NULL);

  g_log_set_handler ("GLib", G_LOG_LEVEL_MASK | G_LOG_FLAG_FATAL
                     | G_LOG_FLAG_RECURSIVE, my_log_handler, NULL);

g_log_remove_handler ()

void        g_log_remove_handler            (const gchar *log_domain,
                                             guint handler_id);

Removes the log handler.

g_log_set_always_fatal ()

GLogLevelFlags g_log_set_always_fatal       (GLogLevelFlags fatal_mask);

Sets the message levels which are always fatal, in any log domain. When a message with any of these levels is logged the program terminates. You can only set the levels defined by GLib to be fatal. G_LOG_LEVEL_ERROR is always fatal.

g_log_set_fatal_mask ()

GLogLevelFlags g_log_set_fatal_mask         (const gchar *log_domain,
                                             GLogLevelFlags fatal_mask);

Sets the log levels which are fatal in the given domain. G_LOG_LEVEL_ERROR is always fatal.

g_log_default_handler ()

void        g_log_default_handler           (const gchar *log_domain,
                                             GLogLevelFlags log_level,
                                             const gchar *message,
                                             gpointer unused_data);

The default log handler. This is used if no log handler has been set for the particular log domain and log level combination. It outputs the message to stderr or stdout and if the log level is fatal it calls abort().

stderr is used for levels G_LOG_LEVEL_ERROR, G_LOG_LEVEL_CRITICAL, and G_LOG_LEVEL_WARNING. stdout is used for the rest. (On the Windows platform, stdout is always used.)