NULL Pointer

NULL pointer:

Literal meaning of NULL pointer is a pointer which is pointing to nothing. NULL pointer points the base address of segment.

Examples of NULL pointer:

1. int *ptr=(char *)0;

2. float *ptr=(float *)0;

3. char *ptr=(char *)0;

4. double *ptr=(double *)0;

5. char *ptr=’\0’;

6. int *ptr=NULL;

What is meaning of NULL?

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:

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");

return 0;
}

Output: I know preprocessor

Explanation:

!NULL = !0 = 1

In if condition any non zero number mean true.

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);


return 0;

}

Output: 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));


return 0;

}

Output: 2

Explanation:

NULL+sizeof(NULL)

=0+sizeoof(0)

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

We cannot copy any thing in the NULL pointer.

Example:

What will be output of following c program?

#include <string.h>
#include <stdio.h>

int main(){

char *str=NULL;

strcpy(str,"c-pointer.blogspot.com");

printf("%s",str);


return 0;

}

Output: (null)