NULL pointer in c programming

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)






Generic pointer

Null pointer
Wild pointer
Dangling pointer
Near pointer
Far pointer
Graphics video memory
Text video memory
Huge pointer
Memory model in C
C tutorial
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