C++ and feature guards Warning Question

[Chris Johns]

On 06/04/2017 07:18, Joel Sherrill wrote:
>
> Trying to compile an open source package for RTEMS, I
> came across something I need help to figure out how
> best to address. The package is in C++ and giving a
> lot of warnings on methods which I would have thought
> are prototyped. But clearly the compiler settings
> are tripping the guards different than the package
> authors expect.
>
> Native GCC on CentOS 7 with glibc gives no warnings.
> It could easily be a GCC version side-effect.
>
> ==========================
> #include <stdlib.h>
>
> int f(char *s)
> {
>   return mkstemp(s);
> }
> ==========================
>
> Warnings with i386-rtems GCC and newilb:
>
> $ i386-rtems4.12-gcc -c j.cc
> $ i386-rtems4.12-gcc -std=c++11 -c j.cc
> j.cc: In function 'int f(char*)':
> j.cc:5:19: error: 'mkstemp' was not declared in this scope
>    return mkstemp(s);
> $ i386-rtems4.12-gcc -std=c++03 -c j.cc
> j.cc: In function 'int f(char*)':
> j.cc:5:19: error: 'mkstemp' was not declared in this scope
>    return mkstemp(s);
> $ i386-rtems4.12-gcc --version
> i386-rtems4.12-gcc (GCC) 6.3.0 20161221 (RTEMS 4.12, RSB
> 4c5eb8969451c4ea0997b3caa98bfe80fe15da69, Newlib 2.5.0.20170228)
>
> Native GCC and glibc results:
>
> $ gcc -std=c++03 -c j.cc
> $ gcc -std=c++11 -c j.cc
> $ gcc -std=c++11 ^C j.cc
> $ gcc --version
> gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-11)
>
> Suggestions on what to do to eliminate the warnings is
> appreciated.
>

I built the code on FreeBSD with clang and the result is the same as Linux:

$ cc -std=c++03 -c j.cc
$ cc -std=c++11 -c j.cc
$ cc --version
FreeBSD clang version 3.8.0 (tags/RELEASE_380/final 262564) (based on 
LLVM 3.8.0)
Target: x86_64-unknown-freebsd11.0
Thread model: posix
InstalledDir: /usr/bin

Adding -save-temps to the builds I see `mkstemp` is guarded with:

#if __MISC_VISIBLE || __POSIX_VISIBLE >= 200112 || __XSI_VISIBLE >= 4

and FreeBSD has:

#if __POSIX_VISIBLE >= 200809 || __XSI_VISIBLE

I hope this helps.

Chris