Re: Forcing the use of 'int' version of strerror_r

[Bob Friesenhahn]

On Wed, 8 Dec 2004, Robert Lowe wrote:

> Hi!
>
> I want to force the use of the POSIX version of strerror_r on systems
> that have two versions.  On GNU/Linux, string.h has the following

My experience with Linux strerror_r (under Linux 2.6.7) is that its 
documentation (man page) is wrong, its behavior is broken, and playing 
with compilation options does not help.  The glibc version always 
seems to return a char *, which is null if it fails.

You would be best served by using configure to learn how the default 
strerror_r behaves and adapting your code to suit.

You don't want to force -D_XOPEN_SOURCE=600 on all systems because 
behavior when the system does not support this level is undefined. 
In my experience, headers on some systems fail miserably if you 
specify an _XOPEN_SOURCE value greater than what they were designed to 
expect.  Using -D_XOPEN_SOURCE=500 is reasonably safe on most (but not 
all) systems.

Trying to force the headers to behave a particular way seems to be a 
lost cause.  After trying this approach for a number of months, I 
finally realized that relying on default behavior worked best.

Bob

> comment:
>
> /* Reentrant version of `strerror'.
>   There are 2 flavors of `strerror_r', GNU which returns the string
>   and may or may not use the supplied temporary buffer and POSIX one
>   which fills the string into the buffer.
>   To use the POSIX version, -D_XOPEN_SOURCE=600 or
>   -D_POSIX_C_SOURCE=200112L
>   without -D_GNU_SOURCE is needed, otherwise the GNU version is
>   preferred.  */
>
> All I can find about the macro is:
>
> Macro: AC_FUNC_STRERROR_R
>    If strerror_r is available, define HAVE_STRERROR_R, and if it is 
> declared, define HAVE_DECL_STRERROR_R. If it returns a char * message, define 
> STRERROR_R_CHAR_P; otherwise it returns an int error number. The Thread-Safe 
> Functions option of POSIX requires strerror_r to return int, but many systems 
> (including, for example, version 2.2.4 of the GNU C Library) return a char * 
> value that is not necessarily equal to the buffer argument.
>
> I'm not assuming that it would be safe to force -D_XOPEN_SOURCE=600
> on all systems, for example, if STRERROR_R_CHAR_P is defined.  What
> combination of tests would be recommended?  Only if $GCC is yes, and
> STRERROR_R_CHAR_P is defined, or is there a test explicitly for
> glibc?  Or something else?  Thanks for your patience... still feeling
> a bit like I've gone down a rabbit hole, and there are way more options
> at this tea party than I imagined.  ;-)
>
> -Robert
>
>
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======================================
Bob Friesenhahn
address@hidden
http://www.simplesystems.org/users/bfriesen