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

[Steve Lhomme]

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...