On 3/29/26 10:58, Yuri wrote:
dnl If the user did not specify a C++ version.
if test -z `echo "$PRESET_CXXFLAGS" | $GREP -o -E "\\-std="`; then
dnl Set highest possible C++ support
AX_CXX_COMPILE_STDCXX(20, [noext], [optional])
if test "$HAVE_CXX20" = "0"; then
AX_CXX_COMPILE_STDCXX(17, [noext], [optional])
elif test "$HAVE_CXX17" = "0"; then
AX_CXX_COMPILE_STDCXX(14, [noext], [optional])
elif test "$HAVE_CXX14" = "0"; then
AX_CXX_COMPILE_STDCXX(11, [noext], [mandatory])
fi
fi
This could be a bug with AX_CXX_COMPILE_STDCXX, in that it is not
checking for C++11 (or whatever) features appropriately. If so, the bug
would be masked in Autoconf 2.70 through 2.72 (which defaulted to C++11
if you did nothing else), but exposed by Autoconf 2.73 (which doesn't
default in that way). Can you investigate this possibility? You should
be a able to do that by looking at config.log.
This is ... about selecting
the highest fully supported standard automatically when the user
provides no flags.
Yes, but Autoconf 2.73 got out of that business, and reverted to its
behavior in Autoconf 2.69 and earlier, for reasons discussed in the top
thread listed here:
https://lists.gnu.org/r/autoconf/2024-05/threads.html
The consensus there, by people who know C++ implementations on GNU/Linux
a lot better than I do, was that Autoconf should not mess with the C++
compiler's default -std= value.
