[FFmpeg-devel] Moving if(constant expression) to preprocessor?

Axel Holzinger aholzinger
Sat Sep 18 18:41:26 CEST 2010

Reimar D?ffinger wrote:
> On Sat, Sep 18, 2010 at 06:00:40PM +0200, Axel Holzinger wrote:
> > You could leave this up to me or others.
> > 
> > It is possible to write a macro that does the trick and in 
> the end the 
> > above line would for example look like this:
> > 
> (av_register_hwaccel(&x##_hwaccel)),)
> > ; }
> > 
> > Wouldn't that still be fine? And it could be done with a 
> few lines of 
> > generic macro defintions that could go to some generic header.
> > 
> > What would be the disadvantage?
> 1) It's a rather obfuscated mess

Where would that mess come from? Please elaborate.

> 2) There's a lot more where this won't work

I don't talk of things that wouldn't work. Please give any details
where what wouldn't work.

> 3) The compiler will not syntax-check (actually it can even
>    run quite a lot of static analysis) the disabled code

Fair enough. But isn't #ifdefs exactly for masking out code that isn't
possible to be compiled on a system that is missing features (like
i.e. hardware support). What more than a function call or struct
definition will the compiler check? I don't think is does help a lot
if the compiler checks this, but leaves away all the details. For
thoroughly checking code, the relies on special features, the features
have to be turned on/be available to get a correct analysis from the

Why is the functions itself masked out by #ifdefs then? Wouldn't it
then be consequent to have function stubs, that do nothing but are
there to make the compiler/linker happy? Using the optimiser to me
does smell a bit.

> And I don't think there's any way you'll be able to solve 3)

No I won't. Sounds like you want to sell this to me as a law that has
to be complied.


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