On 2024-05-01 05:33, Nick Bowler wrote:
Just configure with CFLAGS=-std=c99 or whatever.
I was thinking along the same line. We should keep things simple. Using
CFLAGS is a documented way to specify the compiler flags, and ideally
there would be no need for a new feature in this area.
However, I have some qualms. './configure CFLAGS=-std=c99' works
somewhat by accident, because it tries things in the following order:
echo ' ... C23 test ... ' >conftest.c
gcc -std=c99 conftest.c
gcc -std=gnu23 -std=c99 conftest.c
echo ' ... C11 test ... ' >conftest.c
gcc -std=c99 conftest.c
gcc -std=gnu11 -std=c99 conftest.c
gcc -std:c11 -std=c99 conftest.c
echo ' ... C99 test ... ' >conftest.c
gcc -std=c99 conftest.c
The last GCC invocation is the first one that works, so 'configure'
announces that it has enabled C99 features.
This approach works because GCC treats a later -std= option as
overriding an earlier one. Does the same thing happen with other compilers?
If not, there should be a way for the builder to say "Don't try to mess
with the C standard version; just leave $CC alone". With current
Autoconf on Savannah there's a hacky way to do that:
./configure CC='-std=c99' ac_cv_prog_cc_c23=
but that sort of thing is not something we want to document, as it
depends on the Autoconf version. So perhaps there should be a better way
to disable the C standard version testing that AC_PROG_CC normally does.
