Thanks Ian. Following the link provided by you, I have learned how stddef.h changed to adapt the <sys/_types.h> which first came at FreeBSD 5.
The main change that affects <stddef.h> from <machine/ansi.h> to <sys/_types.h> was explained at http://gcc.gnu.org/ml/gcc/2002-09/msg00560.html What still confuse me is that <stddef.h> doesn't define foo_t by using __foo_t which is defined in either <sys/_types.h> or <machine/_types.h> (mentioned at the link above), the following two links is the corresponding file: http://svnweb.freebsd.org/base/release/5.5.0/sys/sys/_types.h?view=co http://svnweb.freebsd.org/base/release/5.5.0/sys/i386/include/_types.h?view=co Instead, the <stddef.h> uses __FOO_TYPE__ macro to define foo_t, so what makes it necessary to let <stddef.h> include <sys/_types.h> in FreeBSD >= 5 ? I know <stddef.h> will check and define _FOO_T_DECLARED macro which is required by FreeBSD >= 5 in order to claim that foo_t has been declared, but this is not necessarily need to include <sys/_types.h>, right? -- Zachary 2013/5/3 Ian Lance Taylor <i...@google.com>: > On Thu, May 2, 2013 at 3:32 AM, Zachary Jude <zacharyj...@gmail.com> wrote: >> >> I'm figuring out the code in >> >> /usr/lib/gcc/x86_64-redhat-linux/4.1.1/include/stddef.h, >> >> and I saw the macro switch below: >> >> #if defined (__FreeBSD__) && (__FreeBSD__ >= 5) >> #include <sys/_types.h> >> #endif >> >> I have gone through all the <sys/_types>、<sys/cdefs.h> and >> <i386/include/_types.h> source files for the whole 5.X.X version of >> FreeBSD, and still can't find anything may affect the behavior of code >> below that macro switch in <stddef.h>. >> >> Can someone please help in figuring out this ? > > I'm sure you are aware that 4.1.1 is quite old at this point. > > That code was added by this patch: > http://gcc.gnu.org/ml/gcc-patches/2002-10/msg00003.html . Perhaps > that will help explain what is going on here. > > Ian
