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.
G_DISABLE_ASSERTThe 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_CHECKSThis 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_DEBUGQuite 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.
Some of these checks can be relatively expensive at runtime, as they affect every GObject type cast. Distributions are recommended to disable G_ENABLE_DEBUG in stable release builds.
The additional code executed/compiled for this macro currently includes the following, but this is not an exhaustive list:
GDategmessages.c instead of plain abort() to allow debuggers trapping and overriding themgscanner.c to catch deprecated code pathsgutils.c to catch deprecated code pathsgobject.cgsignal.cGTasks