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How to check whether a Macro is defined or not in C?

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mahmoud2506
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2022-05-04
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How to check whether a Macro is defined or not in C?

To check whether a Macro is defined or not in C language – we use #ifdef preprocessor directive, it is used to check Macros only.

Syntax:

    #ifdef MACRO_NAME
	    //body
    #endif

If MACRO_NAME is defined, then the compiler will compile //body (a set of statements written within the #ifdef ... #endif block).

 

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mahmoud2506
2022-05-04
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Example:

#include <stdio.h>

#define NUM 100

int main()
{
	//checking a defined Macro 
	#ifdef NUM
		printf("Macro NUM is defined, and its value is %d\n",NUM);
	#else
		printf("Macro NUM is not defined\n");
	#endif 

	//checking an undefined Macro 
	#ifdef MAX
		printf("Macro MAX is defined, and its value is %d\n",MAX);
	#else
		printf("Macro MAX is not defined\n");
	#endif     

	return 0;
}

Output

    Macro NUM is defined, and its value is 100
    Macro MAX is not defined

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