You can use the #undef preprocessor directive to undefine (override) a previously defined macro.

we can redefine it with the same name and a new value.

Assume 'NULL' is framework defined MACRO. If you wish to override, then,

#ifdef NULL
#undef NULL
#define NULL ((void*)0)
#endif

Above will override already defined MACRO in the scope.

An elegant way of doing this is shown below:

#ifdef MACRO
#undef MACRO
#endif

#define MACRO X

c is a middle level language that come in category of structural programming language so there is no concept of overriding.one method to do this is to #undef the defined macro and then give new definition to macro.

use the #undef preprocessor directive to undefine the define Macros.

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