It is always a good practice to assign a NULL value to a Pointer variable in case you do not have an exact address to be assigned. This is done at the time of variable declaration. A Pointer that is assigned NULL is called a null Pointer. The NULL Pointer is a constant at a value of zero defined in several standard libraries.
Consider the following program:
- #include <stdio.h>
- int main ()
- {
- int *ptr = NULL;
- printf("The value of ptr is : %x\n", &ptr );
- return 0;
- }
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When the above code is compiled and executed, it produces following result:
The value of ptr is 0. On most of the operating systems, programs are not permitted to access memory at address 0 because that memory is reserved by the operating system. However, the memory address 0 has special significance; it signals that the Pointer is not intended to point to an accessible memory location. However, by convention, if a pointer contains the null (zero) value, it is assumed to point to nothing.
To check for a null pointer you can use an if statement as follows:
if(ptr) /* succeeds if p is not null */
if(!ptr) /* succeeds if p is null */ |
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