strnlen, strict ansi, newlib vs glibc

[Thomas Uhle]

On Mon, 2014-09-15 at 13:55 -0500, Joel Sherrill wrote:

> On 9/15/2014 10:12 AM, Thomas Uhle wrote:
> > On Sat, 2014-09-13 at 14:57 +0200, Luca Barbato wrote:
> >
> >> On 14/08/14 17:27, Joel Sherrill wrote:
> >>> Hi
> >>>
> >>> I have some native C++ code that I developed on CentOS and it
> >>> has no warnings. Someone moved it to Cygwin and reported warnings
> >>> for strnlen() not being prototyped. I investigated and the program did
> >>> include string.h. I tried RTEMS tools and got the same as Cygwin
> >>> since we have the same string.h from newlib.
> >>>
> >>> Investigating this, it appears that strnlen() is protected by
> >>> __STRICT_ANSI__ on newlib and  __USE_XOPEN2K8 on Linux.
> >>>
> >>> Command: g++ -Wall -std=c++0x -c strtest.cc
> >>>
> >>> This program is enough to reproduce the issue:
> >>>
> >>>     #include <string.h>
> >>>
> >>>     // size_t strnlen( const char *, size_t );
> >>>
> >>>     size_t f( const char *str )
> >>>     {
> >>>       return strnlen( str, 1000 );
> >>>     }
> >>>
> >>>
> >>> What do you all think?
> >>>
> >> Might be nice to add the support for _DEFAULT_SOURCE with the semantic
> >> of not filter what is on by default notwithstanding the defines -std
> >> might set.
> >>
> >> It seems supported by glibc and musl so might be good to do as well.
> >>
> >> lu
> >>
> > Hello Joel and Luca,
> >
> > I think that the current guard in newlib/libc/include/string.h:119
> >
> > #if !defined(__STRICT_ANSI__) || __XSI_VISIBLE >= 500
> >
> > should be simply replaced by the amended one
> >
> > #if !defined(__STRICT_ANSI__) || __POSIX_VISIBLE >= 200809 || __XSI_VISIBLE >= 700
> >
> > to fix this issue.
> 
>  If Corinna and/or Jeff is OK with this, then I have no issues as
> long as -std=c99 trips the condition based on our cdefs.h. It looks
> like it should.

Actually, strnlen() is part of POSIX.1-2008 (including the X/Open System
Interfaces, Issue 7), but not ISO C99.  Yet, strnlen_s() is part of ISO
C11. So you do not need to specify -std=c99 for strnlen().  Although it
might be necessary to define _POSIX_C_SOURCE=200809 or _XOPEN_SOURCE=700
in your source file before the inclusion of string.h or simply defining
it via option -D in the gcc call.

Best regards,

Thomas Uhle