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cheaderpreprocessor-directive

Undefine a preprocesser directive that is used in another preprocessor directive

This is not my exact issue, but an example is as follows

// Method 1

#define Function(argument)  (StupidLongArray[argument] + OtherStupidLongArrayName[argument] * WhyAreMyNamesSoLong[argument])

or, prefered

// Method 2

#define _SLA StupidLongArray
#define _OSLAN OtherStupidLongArrayName
#define _WAMNSL WhyAreMyNamesSoLong

#define Function(argument) (_SLA[argument] + _OSLAN[argument] * _WAMNSL[argument])

#undef _SLA 
...
...

My understanding of these preprocessor directions implies that once Function has been defined, I can get rid of _SLA and friends. This is not the case.

How come? Is their a way around it?

Solution

  • Unfortunately, there's no way around this. Preprocessor processing basically involves substituting the macro into the original line, then reprocessing it again. So if you call Function(x), it becomes (_SLA[x] + _OSLAN[x] * _WAMNSL[x]) first, then the _SLA, _OSLAN, and _WAMNSL macros are substituted afterward. If they're not defined at the place where this substitution occurs, they'll be left as is.