Re: Macro to cause build failure if parameter not defined?

skillzero@xxxxxxxxx wrote:
Is there a way to cause a compile/preprocessor error in a macro if a
preprocessor symbol is not defined? I want to do the equivalent of
this in a macro:

#if( !defined( SOME_FLAG ) )
#error not defined
#endif

What I want is a way to test if a feature flag is defined to 1 such
that if it's not defined at all (as opposed to defined to 0), I'll get
a compile error. This is to catch cases where people test for a
feature flag without including the right header file, using the right
compile flags, or they just typed it wrong. I want to use it like
this:

#if( HAS_FEATURE( FEATURE_X ) )
... do something if FEATURE_X is defined
#endif

I'll #define FEATURE_X to 1 if supported or #define FEATURE_X to 0 if
not suported. If not defined at all, I want to generate a compile
error.

I think

#define HAS_FEATURE(macro) ( (macro) / defined(macro) )

.... might suit you, if you don't mind an uninformative or maybe
even misleading diagnostic.

--
Eric Sosman
esosman@xxxxxxxxxxxxxxxxxxxx
.

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