On 09/27/2012 07:29 AM, Adrian Bunk wrote: > glibc 2.16 has the following protected by what boils down to > #if defined _GNU_SOURCE || defined _ISOC11_SOURCE || \ > (defined __STDC_VERSION__ && __STDC_VERSION__ >= 201112L) > > - timespec_get() and TIME_UTC > - aligned_alloc() > - at_quick_exit() > - quick_exit() > - CMPLX/CMPLXF/CMPLXL > - static_assert
Thanks for mentioning that. I'd missed those. Normally this is considered part of the C library, not of the C compiler, so AC_PROG_CC shouldn't check for it. But it is an argument for people using either AC_PROG_CC or AC_USE_SYSTEM_EXTENSIONS, so that they can get the above symbols. (This is true for older versions of Autoconf too, for AC_USE_SYSTEM_EXTENSIONS.) > It's a policy decision which features should be guaranteed to be > available when ac_cv_prog_cc_c11 is not "no" Yes, that's the dicey thing. AC_PROG_CC doesn't really guarantee C11 (or C99 or C89); it merely tries to do its best to make the compiler more up-to-date. In effect, Autoconf is warring against the understandable conservativism of compiler implementers. Autoconf-generated programs want the latest and greatest version, whereas compiler-writers are often concerned that the latest version will break ancient programs. Hence compiler-writers are often too- conservative about setting defaults, from Autoconf's point of view, and Autoconf is striving to overcome that. The features Autoconf are testing for are a means to an end (getting more-up-to-date compiler), not the end itself (a list of supported features; there is no such list, really).
