What is meaning of NULL?

What is meaning of NULL?

Answer:

NULL is macro constant which has been defined in the heard file stdio.h, alloc.h, mem.h, stddef.h and stdlib.h as

#define NULL 0

Examples:

(1)What will be output of following c program?

#include "stdio.h"

int main(){

if(!NULL)

printf("I know preprocessor");

else

printf("I don't know preprocessor");

}

Output: I know preprocessor

Explanation:

!NULL = !0 = 1

In if condition any non zero number mean true.

(2)What will be output of following c program?

#include "stdio.h"

int main(){

int i;

static int count;

for(i=NULL;i<=5;){

count++;

i+=2;

}

printf("%d",count);

}

Output: 3

(3)What will be output of following c program?

#include "stdio.h"

int main(){

#ifndef NULL

#define NULL 5

#endif

printf("%d",NULL+sizeof(NULL));

}

Output: 2

Explanation:

NULL + sizeof(NULL)

=0 + sizeoof(0)

=0+2 //size of int data type is two byte.

We cannot copy anything in the NULL pointer.

Example:

(4)What will be output of following c program?

#include "string.h"

int main(){

char *str=NULL;

strcpy(str,"hello");

printf("%s",str);

return 0;

}

Output: (null)

Blog Author: Vijay Kumar

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