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c preprocessor ifdef

The #ifdef is a preprocessor directive in C which is used to execute a piece of code, only if the specified macro is already defined by #define.


#ifdef MACRO

// code to be executed if macro is defined



#ifdef MACRO

// code to be executed if macro is defined


// code to be executed if macro is not defined



#define E 2.718
void main()
#ifdef E
printf("E: %f", E);
printf("E is not defined.");  


E: 2.718000
Posted in C   
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