glib/docs/macros.md

GLib's configure options and corresponding macros

The following Meson configure options will result in certain macros or options being defined at build time:

--buildtype={plain,release,minsize,custom} : No special macros or options --buildtype={debug,debugoptimized} (debugoptimized is the default) : -DG_ENABLE_DEBUG -g -Dglib_debug=disabled : Omits G_ENABLE_DEBUG when implied by --buildtype/-Ddebug -Dglib_debug=enabled : Defines G_ENABLE_DEBUG regardless of --buildtype/-Ddebug -Dglib_asserts=false : -DG_DISABLE_ASSERT -Dglib_checks=false : -DG_DISABLE_CHECKS

Besides these, there are some local feature specific options, but the main focus here is to concentrate on macros that affect overall GLib behaviour and/or third party code.

GLib's internal and global macros

G_DISABLE_ASSERT

The g_assert() and g_assert_not_reached() macros become non-functional with this define. The motivation is to speed up end-user apps by avoiding expensive checks.

This macro can affect third-party code. Defining it when building GLib will only disable the assertion macros for GLib itself, but third-party code that passes -DG_DISABLE_ASSERT to the compiler in its own build will end up with the non-functional variants after including glib.h as well.

Note: Code inside the assertion macros should not have side effects that affect the operation of the program, as they may get compiled out.

G_DISABLE_CHECKS

This macro is similar to G_DISABLE_ASSERT, it affects third-party code as mentioned above and the note about G_DISABLE_ASSERT applies too.

The macros that become non-functional here are g_return_if_fail(), g_return_val_if_fail(), g_return_if_reached() and g_return_val_if_reached().

This macro also switches off certain checks in the GSignal code.

G_ENABLE_DEBUG

Quite a bit of additional debugging code is compiled into GLib when this macro is defined, and since it is a globally visible define, third-party code may be affected by it similarly to G_DISABLE_ASSERT.

The additional code executed/compiled for this macro currently includes the following, but this is not an exhaustive list:

• extra validity checks for GDate
• breakpoint abortion for fatal log levels in gmessages.c instead of plain abort() to allow debuggers trapping and overriding them
• added verbosity of gscanner.c to catch deprecated code paths
• added verbosity of gutils.c to catch deprecated code paths
• object and type bookkeeping in gobject.c
• extra validity checks in gsignal.c
• support for tracking still-alive GTasks