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How to check whether a Macro is defined or not in C?
Here, we will learn how to check whether a Macro is defined or not in C? To check – A Macro is defined or not, we use #ifdef preprocessor directive.
By IncludeHelp Last updated : March 10, 2024
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).
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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