C Preprocessor Operator: defined

In this video tutorial lets see how to use preprocessor operator “defined” in C programming language.

How Does ‘defined’ preprocessor operator work?

defined preprocessor operator can only be used with #if and #elif directives.

If the Macro name passed to define is actually defined, then it returns true or else it’ll return false.

Syntac of “defined”

#if( defined(macro_name1) )
  // Some Set of Code
#elif( defined(macro_name2) )
  // Some More Set of Code
#endif

OR

#if defined(macro_name1) 
  // Some Set of Code
#elif defined(macro_name2) 
  // Some More Set of Code
#endif

Video Tutorial: C Preprocessor Operator: defined

Source Code: C Preprocessor Operator: defined

#include<stdio.h>

#define PI 3.14159265358979323846

#define AREA

void area_circle(float r);
void circumference_circle(float r);

int main()
{
    float r;

    printf("Enter radius of Circle\n");
    scanf("%f", &r);

    #if defined(AREA)
        area_circle(r);
    #elif defined(CIRCUM)
        circumference_circle(r);
    #else
        printf("Code To Be Implemented\n");

    #endif // defined

    return 0;
}

void area_circle(float r)
{
    printf("Area of Circle is %f\n", (PI * r * r) );
}

void circumference_circle(float r)
{
    printf("Circumference of Circle is %f\n", (2 * PI * r) );
}

Output:
Enter radius of Circle
5
Area of Circle is 78.539816

In above source code AREA macro template or macro name is defined. So defined(AREA) returns true in #if condition. Hence the code inside #if block gets compiled and executed.

#include<stdio.h>

#define PI 3.14159265358979323846

#define CIRCUM

void area_circle(float r);
void circumference_circle(float r);

int main()
{
    float r;

    printf("Enter radius of Circle\n");
    scanf("%f", &r);

    #if defined(AREA)
        area_circle(r);
    #elif defined(CIRCUM)
        circumference_circle(r);
    #else
        printf("Code To Be Implemented\n");

    #endif // defined

    return 0;
}

void area_circle(float r)
{
    printf("Area of Circle is %f\n", (PI * r * r) );
}

void circumference_circle(float r)
{
    printf("Circumference of Circle is %f\n", (2 * PI * r) );
}

Output:
Enter radius of Circle
5
Circumference of Circle is 31.415927

Here macro name AREA is not defined, hence code inside #if gets skipped. Whereas macro CIRCUM is defined, so the code inside #elif gets compiled and executed.

If neither AREA and nor CIRCUM is defined, then code inside #else block gets compiled and executed.

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