In this video tutorial lets see how to use preprocessor operator “defined” in C programming language.
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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
[youtube https://www.youtube.com/watch?v=IDiV22rMPBk]
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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