This example contains a small hack in AC_PROG_CC_C11 to emulate the situation when [1] will be fixed.
<-- snip --> $ autoconf --version autoconf (GNU Autoconf) 2.69.22-787a ... $ cat configure.ac AC_INIT AC_PROG_CC_C99 AC_PROG_CC_C11 $ ./configure checking for gcc... gcc checking whether the C compiler works... yes checking for C compiler default output file name... a.out checking for suffix of executables... checking whether we are cross compiling... no checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ISO C89... none needed checking for gcc option to accept ISO C99... -std=gnu99 checking for gcc -std=gnu99 option to accept ISO C11... -std=gnu11 $ grep ^CC config.log CC='gcc -std=gnu99 -std=gnu11' $ <-- snip --> I don't think this chaining of options is a desired and always working situation, and I would be completely non-surprised it e.g. an AIX compiler would choke on "-qlanglvl=extc89 -qlanglvl=extc99" and never reach any mode higher than C89. Note that this not an exotic situation since AC_PROG_CC_C99 and AC_PROG_CC_C11, and therefore also AC_PROG_CC_STDC, first run the C89 check and add options for C89 if needed (through AC_PROG_CC I assume), and only after that run any C99/C11 checks. cu Adrian [1] http://lists.gnu.org/archive/html/bug-autoconf/2012-09/msg00007.html -- "Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed
