g_print ()

void
g_print (const gchar *format,
         ...);

Outputs a formatted message via the print handler. The default print handler simply outputs the message to stdout, without appending a trailing new-line character. Typically, format should end with its own new-line character.

g_print() should not be used from within libraries for debugging messages, since it may be redirected by applications to special purpose message windows or even files. Instead, libraries should use g_log(), g_log_structured(), or the convenience macros g_message(), g_warning() and g_error().

g_set_print_handler ()

GPrintFunc
g_set_print_handler (GPrintFunc func);

Sets the print handler.

Any messages passed to g_print() will be output via the new handler. The default handler simply outputs the message to stdout. By providing your own handler you can redirect the output, to a GTK+ widget or a log file for example.

GPrintFunc ()

void
(*GPrintFunc) (const gchar *string);

Specifies the type of the print handler functions. These are called with the complete formatted string to output.

g_printerr ()

void
g_printerr (const gchar *format,
            ...);

Outputs a formatted message via the error message handler. The default handler simply outputs the message to stderr, without appending a trailing new-line character. Typically, format should end with its own new-line character.

g_printerr() should not be used from within libraries. Instead g_log() or g_log_structured() should be used, or the convenience macros g_message(), g_warning() and g_error().

g_set_printerr_handler ()

GPrintFunc
g_set_printerr_handler (GPrintFunc func);

Sets the handler for printing error messages.

Any messages passed to g_printerr() will be output via the new handler. The default handler simply outputs the message to stderr. By providing your own handler you can redirect the output, to a GTK+ widget or a log file for example.

g_return_if_fail()

#define             g_return_if_fail(expr)

Verifies that the expression expr , usually representing a precondition, evaluates to TRUE. If the function returns a value, use g_return_val_if_fail() instead.

If expr evaluates to FALSE, the current function should be considered to have undefined behaviour (a programmer error). The only correct solution to such an error is to change the module that is calling the current function, so that it avoids this incorrect call.

To make this undefined behaviour visible, if expr evaluates to FALSE, the result is usually that a critical message is logged and the current function returns.

If G_DISABLE_CHECKS is defined then the check is not performed. You should therefore not depend on any side effects of expr .

To debug failure of a g_return_if_fail() check, run the code under a debugger with G_DEBUG=fatal-criticals or G_DEBUG=fatal-warnings defined in the environment (see Running GLib Applications):

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G_DEBUG=fatal-warnings gdb ./my-program

Any unrelated failures can be skipped over in gdb using the continue command.

g_return_val_if_fail()

#define             g_return_val_if_fail(expr,val)

Verifies that the expression expr , usually representing a precondition, evaluates to TRUE. If the function does not return a value, use g_return_if_fail() instead.

If expr evaluates to FALSE, the current function should be considered to have undefined behaviour (a programmer error). The only correct solution to such an error is to change the module that is calling the current function, so that it avoids this incorrect call.

To make this undefined behaviour visible, if expr evaluates to FALSE, the result is usually that a critical message is logged and val is returned from the current function.

If G_DISABLE_CHECKS is defined then the check is not performed. You should therefore not depend on any side effects of expr .

See g_return_if_fail() for guidance on how to debug failure of this check.

g_return_if_reached

#define             g_return_if_reached()

Logs a critical message and returns from the current function. This can only be used in functions which do not return a value.

See g_return_if_fail() for guidance on how to debug failure of this check.

g_return_val_if_reached()

#define             g_return_val_if_reached(val)

Logs a critical message and returns val .

See g_return_if_fail() for guidance on how to debug failure of this check.

g_warn_if_fail()

#define             g_warn_if_fail(expr)

Logs a warning if the expression is not true.

Since: 2.16

g_warn_if_reached

#define             g_warn_if_reached()

Logs a warning.

Since: 2.16

g_on_error_query ()

void
g_on_error_query (const gchar *prg_name);

Prompts the user with [E]xit, [H]alt, show [S]tack trace or [P]roceed. This function is intended to be used for debugging use only. The following example shows how it can be used together with the g_log() functions.

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#include <glib.h>

static void
log_handler (const gchar   *log_domain,
             GLogLevelFlags log_level,
             const gchar   *message,
             gpointer       user_data)
{
  g_log_default_handler (log_domain, log_level, message, user_data);

  g_on_error_query (MY_PROGRAM_NAME);
}

int
main (int argc, char *argv[])
{
  g_log_set_handler (MY_LOG_DOMAIN,
                     G_LOG_LEVEL_WARNING |
                     G_LOG_LEVEL_ERROR |
                     G_LOG_LEVEL_CRITICAL,
                     log_handler,
                     NULL);
  ...

If "[E]xit" is selected, the application terminates with a call to _exit(0).

If "[S]tack" trace is selected, g_on_error_stack_trace() is called. This invokes gdb, which attaches to the current process and shows a stack trace. The prompt is then shown again.

If "[P]roceed" is selected, the function returns.

This function may cause different actions on non-UNIX platforms.

On Windows consider using the G_DEBUGGER environment variable (see Running GLib Applications) and calling g_on_error_stack_trace() instead.

g_on_error_stack_trace ()

void
g_on_error_stack_trace (const gchar *prg_name);

Invokes gdb, which attaches to the current process and shows a stack trace. Called by g_on_error_query() when the "[S]tack trace" option is selected. You can get the current process's program name with g_get_prgname(), assuming that you have called gtk_init() or gdk_init().

This function may cause different actions on non-UNIX platforms.

When running on Windows, this function is *not* called by g_on_error_query(). If called directly, it will raise an exception, which will crash the program. If the G_DEBUGGER environment variable is set, a debugger will be invoked to attach and handle that exception (see Running GLib Applications).

G_BREAKPOINT

#  define G_BREAKPOINT()        G_STMT_START{ __asm__ __volatile__ ("int $03"); }G_STMT_END

Inserts a breakpoint instruction into the code.

On architectures which support it, this is implemented as a soft interrupt and on other architectures it raises a SIGTRAP signal.

SIGTRAP is used rather than abort() to allow breakpoints to be skipped past in a debugger if they are not the desired target of debugging.