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Asked: 2026-06-01T03:05:28+00:00

Wanted to understand the difference between undef and define a macro as 0. Thanks.

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Wanted to understand the difference between undef and define a macro as 0. Thanks.

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1 Answer

  1. Editorial Team
    #define MACRO 0

    defines the preprocessor token MACRO to be the literal 0

    #undef MACRO

    Removes the definition of the preprocessor token MACRO so that it’s as if it never existed.

    For example:

    #define MACRO 0

#if defined ( MACRO )
// we get here
#endif

#if ( MACRO )
// we don't get here
#endif

#undef MACRO

#if defined ( MACRO )
// we don't get here
#endif
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