[Ffmpeg-devel] [PATCH] from DivX, Part 7: MSVC fixes

[Rich Felker]

On Wed, Jan 25, 2006 at 01:32:00PM -1000, Steve Lhomme wrote:
> 
> 
> Rich Felker wrote:
> >On Wed, Jan 25, 2006 at 10:09:17AM -1000, Steve Lhomme wrote:
> >>>>>+#if __STDC_VERSION__ >= 199901L
> >>>>>    uint8_t fixed[s->mb_stride * s->mb_height];
> >>>>>+#else
> >>>>>+    uint8_t *fixed=(uint8_t*)alloca(s->mb_stride * s->mb_height);
> >>>>>+#endif
> >>>>rejected
> >>>>
> >>>>#define A(type, name, size) type name[size];
> >>>>#define A(type, name, size) type *name= alloca(size * sizeof(type));
> >>>>
> >>>>would be cleaner but even then i would say that needs some disscussion 
> >>>>and
> >>>>should be a seperate patch
> >>>This is a somewhat dangerous thing to do, since it makes sizeof(name)
> >>>unpredictable.
> >>I just checked, all the variables with this kind of change are never 
> >>used with sizeof().
> >
> >alloca is not portable. Moreover the 'portable' alloca dropin for
> >systems missing it is implemented with malloc and evil garbage
> >collection hacks meaning it will cause memleaks.
> >
> >C99 has vla's for a reason. It also lacks alloca for a reason. Don't
> >use legacy nonportable crap in place of proper standards to work
> >around MS's unwillingness to adhere to modern standards.
> 
> Hence the reason to only use alloca() for older compilers...

Yes but you also need to use vla for all versions of gcc, since even
the pre-C99 ones (especially 2.95 :) support vla.

Rich