Warnings and Assertions
Warnings and Assertions
GLib defines several warning functions and assertions which can be used to warn of programmer errors when calling functions, and print error messages from command line programs.
Pre-condition Assertions
The g_return_if_fail(), g_return_val_if_fail(),
g_return_if_reached() and g_return_val_if_reached() macros are
intended as pre-condition assertions, to be used at the top of a public function
to check that the function’s arguments are acceptable. Any failure of such a
pre-condition assertion is considered a programming error on the part of the
caller of the public API, and the program is considered to be in an undefined
state afterwards. They are similar to the libc assert()
function, but provide more context on failures.
For example:
gboolean
g_dtls_connection_shutdown (GDtlsConnection *conn,
gboolean shutdown_read,
gboolean shutdown_write,
GCancellable *cancellable,
GError **error)
{
// local variable declarations
g_return_val_if_fail (G_IS_DTLS_CONNECTION (conn), FALSE);
g_return_val_if_fail (cancellable == NULL || G_IS_CANCELLABLE (cancellable), FALSE);
g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
// function body
return return_val;
}
g_warn_if_fail() and g_warn_if_reached() behave similarly, but
they will not abort the program on failure. The program should be considered to
be in an undefined state if they fail, however.
Messages
g_print() and g_printerr() are intended to be used for
output from command line applications, since they output to standard output
and standard error by default — whereas functions like g_message() and
g_log() may be redirected to special purpose message windows, files, or
the system journal.
The default print handlers may be overridden with g_set_print_handler()
and g_set_printerr_handler().
Encoding
If the console encoding is not UTF-8 (as specified by
g_get_console_charset()) then these functions convert the message first.
Any Unicode characters not defined by that charset are replaced by '?'. On
Linux, setlocale() must be called early in main() to
load the encoding. This behaviour can be changed by providing custom handlers to
g_set_print_handler(), g_set_printerr_handler() and
g_log_set_handler().