[MPlayer-dev-eng] [PATCH] libvo: GGI driver update

[Christoph Egger]

> Christoph Egger wrote:
> > "if (arg)" is wrong, because it compares against the _number_ != 0,
> > but arg is a pointer. See below.
> 
> No zero is special, see C99 6.3.2.3.3:
> 
>     An integer constant expression with the value 0, or such an
>     expression cast to type void *, is called a null pointer constant...
> 
> if (arg) is not wrong.  The C++ standard is more clear about this, as it
> type-converts to bool and there are clear rules about the conversion.  It
> seems that C99 just says it's the same as (arg != 0), but by the above
> paragraph, 0 is clearly a legal null pointer constant.  Off topic, but in
> C++ NULL is often just #define to 0 because (void*)0 cannot be implicitly
> converted to other pointer types.

bool is a new datatype in C, since C99. It has been backported from
C++. In C++, NULL was thrown away or is a just a #define to 0 to make
migration from C to C++ easier. The C++ standard says, the compiler
autodetects this and handles this right.

With the introduction of the bool type in C99, same counts for C
(if the compiler supports this - most compilers still support C99
_partially_).

Now the question is, what requires (or better prefers) mplayer?
C89 or C99?

If C89, then "if (arg != NULL)" is the only correct thing.
If C99, then "if (arg)" is fine with me.

Personally, I still prefer C89 for more portability,
because compilers still have no complete C99 support.

> > I already experienced many bugs that caused stack and
> > heap corruption just by mixing up pointers with numbers
> > - in particular on 64bit platforms.
> 
> Yes, but not this one.
> 
> > > It's not a bug unless it can possibly lead to wrong behavior.
> > 
> > My understanding of what is a bug is more restrictive:
> 
> if (arg) is a very common C idiom.  IMO if (arg != NULL) is not any
> easier to read than if (arg).

See above.

-- 
Greetings,

Christoph

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