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cdefs.9: Update for C++ environments

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We support all the C++ standards to some degree. However, pre C++11
standard support has been disappearing upstream, so also add a note
about -pedantic-errors might not work for earlier standards. Add note
about __cplusplus values.

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This commit is contained in:
Warner Losh 2024-07-20 08:38:52 -06:00
parent 00266393cc
commit eaa3d34b62
1 changed files with 41 additions and 2 deletions
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43
share/man/man9/cdefs.9
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@ -3,7 +3,7 @@
.\"
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.Dd July 18, 2024
.Dd July 20, 2024
.Dt CDEFS 9
.Os
.Sh NAME
@ -281,7 +281,7 @@ still uses these.
supports a number C standard environments.
Selection of the language dialect is a compiler-dependent command line option,
though it is usually
.Fl cstd=XX
.Fl std=XX
where XX is the standard to set for compiling, such as c89 or c23.
.Fx
provides a number of selection macros to control visibility of symbols.
@ -402,6 +402,45 @@ extensions are visible, 0 otherwise.
.St -isoC-2011
Appendix K 3.7.4.1
extensions are visible, 0 otherwise.
.Sh Supported C++ Environments
.Fx
supports C++11 and newer standards fully.
.Bl -tag
.It ISO/IEC 14882:1998 ("C++98")
.Dv __cplusplus = 199711
.Pp
The first standardized version of C++.
Unlike K \*(Am R support in C, compilers dropped support for versions of
the language prior to C++98.
.It ISO/IEC 14882:2003 ("C++03")
.Dv __cplusplus = 199711
.Pp
Note, this is the same value as C++98.
C++03 did not define a new value for
.Dv __cplusplus .
There is no way, at compile time, to detect the difference.
The standard resolved a number of defect reports and slightly
expanded value initialization.
Most compilers support it the same as C++98.
.It ISO/IEC 14882:2011 ("C++11")
.Dv __cplusplus = 201103
.It ISO/IEC 14882:2014 ("C++14")
.Dv __cplusplus = 201402
.It ISO/IEC 14882:2017 ("C++17")
.Dv __cplusplus = 201703
.It ISO/IEC 14882:2020 ("C++20")
.Dv __cplusplus = 202002
.It ISO/IEC 14882:2023 ("C++23")
.Dv __cplusplus = 202302
.El
.Pp
.Fx
uses llvm project's libc++.
However, they are removing support for C++ prior to C++11.
While programs can still build with earlier environments for now, these changes
mean that
.Fl pedantic-errors
cannot be reliably enabled for standards older than C++11.
.Sh HISTORY
.In sys/cdefs.h
first appeared in