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

Måns Rullgård mans
Sat Sep 18 13:20:56 CEST 2010

"Axel Holzinger" <aholzinger at gmx.de> writes:

> Hi all,
> if compiling FFmpeg code with zero optimisations (even without dead
> code elimination) there are linker errors (undefined references to
> functions or structs) that come from constructs like i.e. the
> following in libavcodec/allcodecs.c:
> if(CONFIG_##X##_HWACCEL) av_register_hwaccel(&x##_hwaccel); )
> The runtime (lower case) "if" leads to an undefined reference, because
> it is evaluated at runtime and not at compile time.
> If dead code eliminitation optimisation is on, this isn't an issue,
> but with optimisations completely off it is.

Don't do that then.

> Is there interest in doing this in a way where already the
> preprocessor is solving this (instead of the optimiser)?


> Then I would try and find a solution based on preprocessor magic.

That is not easily possible.

M?ns Rullg?rd
mans at mansr.com

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