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An Example of Null pointer in C

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mahmoud2506
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2022-05-04
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An Example of Null pointer in C

NULL pointer

The word "NULL" is a constant in C language and its value is 0. In case with the pointers - if any pointer does not contain a valid memory address or any pointer is uninitialized, known as "NULL pointer". We can also assign 0 (or NULL) to make a pointer as "NULL pointer".

Example:

In this example, there are 3 integer pointers ptr1, ptr2 and ptr3. ptr1 is initialized with the address of the integer variable num, thus ptr1 contains a valid memory address. ptr2 is uninitialized and ptr3 assigned 0. Thus, ptr2 and ptr3 are the NULL pointers.

 

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mahmoud2506
2022-05-04
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Program:

#include <stdio.h>

int main(void) {
	int num = 10;

	int *ptr1 = &num;
	int *ptr2;
	int *ptr3=0;

	if(ptr1 == 0)
		printf("ptr1: NULL\n");
	else
		printf("ptr1: NOT NULL\n");

	if(ptr2 == 0)
		printf("ptr2: NULL\n");
	else
		printf("ptr2: NOT NULL\n");

	if(ptr3 == 0)
		printf("ptr3: NULL\n");
	else
		printf("ptr3: NOT NULL\n");

	return 0;
}

Output

ptr1: NOT NULL 
ptr2: NULL 
ptr3: NULL

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