[help-gengetopt] Re: GNU Gengetopt 2.22

[Lorenzo Bettini]

Andre Noll wrote:
> > > Similarly, if gengetopt is compiled on Mac, and then configured and
> > > built on Linux, it results in
> > >
> > >         argsdef.o: file not recognized: File format not recognized
> > >         
> > > However, this is not a serious issue because "make clean" solves the
> > > problem.
> > mh... I don't think this is the expected behavior: issueing another 
> > configure might change the config.h and the files that include it will 
> > be recompiled, but not all files are expected to include it; actually if 
> > you build a package for different platforms you should run each 
> > configure in a separate directory (one for each different configure).
>
> OK. Another solution would be to let all object files depend on Makefile
> which is also generated by configure.

mhh... but I don't know whether this can be made in a clean way with 
autotools...  I'm pretty sure that configure for different architectures 
should be run in different directories...

> > > Finally, when compiling audiod.cmdline.c, a file generated by
> > > gengetopt-2.22, I see the following warning, which didn't show up
> > > when using earlier versions of gengetopt:
> > >
> > > audiod.cmdline.c: In function 'audiod_cmdline_parser_release':
> > > audiod.cmdline.c:337: warning: dereferencing type-punned pointer will 
> > > break strict-aliasing rules
> > >
> > > The offending line 337 in audiod.cmdline.c is
> > >
> > > 	  free_multiple_field (args_info->user_allow_given, (void 
> > > 	  **)&(args_info->user_allow_arg), &(args_info->user_allow_orig));
> > >
> > > And free_multiple_field() looks like this:
> > >
> > > static void
> > > free_multiple_field(unsigned int len, void **arg, char ***orig)
> > > {
> > >  unsigned int i;
> > >  if (*arg) {
> > >    for (i = 0; i < len; ++i)
> > >      {
> > >        free_string_field(&((*orig)[i]));
> > >      }
> > >
> > >    free (*arg);
> > >    *arg = 0;
> > >    free (*orig);
> > >    *orig = 0;
> > >  }
> > > }
> > >
> > > Why you are using void ** as the second parameter "arg" when the function
> > > is only using *arg? Wouldn't it be better to generate
> > >
> > > static void
> > > free_multiple_field(unsigned int len, void *arg, char ***orig)
> > > {
> > >  unsigned int i;
> > >  if (arg) {
> > >    for (i = 0; i < len; ++i)
> > >      {
> > >        free_string_field(&((*orig)[i]));
> > >      }
> > >
> > >    free (arg);
> > >    free (*orig);
> > >    *orig = 0;
> > >  }
> > > }
> > >
> > > instead? This would allow to get rid of the cast in the offending line.
> > > The only drawback I can see is that args_info->user_allow_arg is not
> > > set to NULL by free_multiple_field() when using this approach.
> > mh... setting that arg to null is crucial (since what is freed could be 
> > re-used internally), but probably I could set it to NULL after that 
> > function call, I'll take a look at this.
>
> I see. An alternative for getting rid of this warning is to introduce an
> intermediate (void *) cast:
>
>         free_multiple_field (args_info->user_allow_given, (void **)(void 
> *)&(args_info->user_allow_arg), &(args_info->user_allow_orig));
>                                                                    ^^^^^^^^

well if this does not generate the warning I think that'd be a better 
solution :-)

> > Actually, I don't get this warning, so thanks for reporting it.
>
> You need to compile with -Wstrict-aliasing (included in -Wall) and
> with -fstrict-aliasing (enabled at levels -O2, -O3, -Os).

actually I always test compilations with -Wall but I don't get this 
warning... probably because you're using a different architecture?  Is 
this warning something to worry about?  I mean: I want to remove it, but 
does the warning means that the above code can do something wrong?

thanks
        Lorenzo

P.S. there are also other warnings that I still need to remove; Gyozo, I 
didn't remember to remove all the warnings you told me about; I'll do 
that in the very near future :-)

--
Lorenzo Bettini, PhD in Computer Science, DI, Univ. Torino
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