#undef in c

Explanation of #undef directives in c programming language by
examples, questions and answers



Directive #undef is used
to undefine any macro constants except global identifiers. It is useful when we
want to redefined any macro constants. For example:



#include

#define ABC
25

#ifdef ABC

#undef ABC

#define ABC 50

#else

#define ABC 100

#endif



int main(){

printf("%d"