It is always a good practice to assign the pointer NULL to a pointer variable in case you do not
have 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 with a value of zero defined in several standard libraries,
including iostream. Consider the following program:
using namespace std;
int main ()
int *ptr = NULL;
cout << "The value of ptr is " << ptr ;
When the above code is compiled and executed, Output Will Be :
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. But 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
Thus, if all unused pointers are given the null value and you avoid the use of a null pointer,
you can avoid the accidental misuse of an uninitialized pointer. Many times uninitialized
variables holds some junk values and it becomes difficult to debug the program.
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