mainAutoconf - Support: sr #110879, revert forcing/setting...


sr #110879: revert forcing/setting -std=gnu++11 by default (introduced in Autoconf 2.70)

Submitter:  Jörn Heusipp <manx>
Submitted:  Sun 07 May 2023 07:26:46 AM UTC
Category:  None Priority:  5 - Normal
Severity:  4 - Important Status:  None
Privacy:  Public Assigned to:  None
Open/Closed:  Open Operating System:  None
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Sun 07 May 2023 07:28:33 AM UTC, comment #1: 
Jörn Heusipp <manx>
Sun 07 May 2023 07:26:46 AM UTC, original submission:  

> * Noteworthy changes in release 2.70 (2020-12-08) [stable]


> * AC_PROG_CC now enables C2011 mode if the compiler supports it.
>   If not, it will fall back to C99 and C89, as before.  Similarly,
>   AC_PROG_CXX now enables C++2011 if available, falling back on C++98.

This breaks existing packages that have been relying on `AX_CXX_COMPILE_STDCXX` from the autoconf-archive package (<>) since about forever, because Autoconf itself did never care about the C++ standard version at all.

There appears to be no documentation on how to avoid the introduced behaviour, as far as I can see.

The new behaviour causes CXXFLAGS to look like '-std=gnu++11 -std=c++20', which is just confusing and arguably outright wrong.

In other cases, where the compiler default is actually newer than C++11 (e.g. GCC6 defaults to C++14, GCC11 defaults to C++17), it actively breaks compilation for programs that simply rely on the toolchain default.

See <>.

Please revert this change.

Jörn Heusipp <manx>


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