because:
- GeHint return a value pointer.
- SetHint free internally the pointer
- The -now invalid- pointer is re-read
==9363== Invalid read of size 1
==9363== at 0x4946860: SW_CreateRenderer (SDL_render_sw.c:1044)
==9363== by 0x48F0EC3: SDL_CreateRenderer_REAL (SDL_render.c:938)
==9363== by 0x48C5921: SDL_CreateRenderer (SDL_dynapi_procs.h:332)
==9363== by 0x401584: main (main.c:421)
==9363== Address 0x9c24040 is 0 bytes inside a block of size 1 free'd
==9363== at 0x484621F: free (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==9363== by 0x494E403: SDL_free_REAL (SDL_malloc.c:5432)
==9363== by 0x48A6153: SDL_SetHintWithPriority_REAL (SDL_hints.c:76)
==9363== by 0x48A6254: SDL_SetHint_REAL (SDL_hints.c:101)
Case fallthrough warnings can be suppressed using the __fallthrough__
compiler attribute. Unfortunately, not all compilers have this
attribute, or even have __has_attribute to check if they have the
__fallthrough__ attribute. [[fallthrough]] is also available in C++17
and the next C2x, but not everyone uses C++17 or C2x.
So define the SDL_FALLTHROUGH macro to deal with those problems - if we
are using C++17 or C2x, it expands to [[fallthrough]]; else if the
compiler has __has_attribute and has the __fallthrough__ attribute, then
it expands to __attribute__((__fallthrough__)); else it expands to an
empty statement, with a /* fallthrough */ comment (it's a do {} while
(0) statement, because users of this macro need to use a semicolon,
because [[fallthrough]] and __attribute__((__fallthrough__)) require a
semicolon).
Clang before Clang 10 and GCC before GCC 7 have problems with using
__attribute__ as a sole statement and warn about a "declaration not
declaring anything", so fall back to using the /* fallthrough */ comment
if we are using those older compiler versions.
Applications using SDL are also free to use this macro (because it is
defined in begin_code.h).
All existing /* fallthrough */ comments have been replaced with this
macro. Some of them were unnecessary because they were the last case in
a switch; using SDL_FALLTHROUGH in those cases would result in a compile
error on compilers that support __fallthrough__, for having a
__attribute__((__fallthrough__)) statement that didn't immediately
precede a case label.
