A pointer to a pointer is a form of multiple indirection or a chain of pointers.
Normally, a pointer contains the address of a variable. When we define a pointer
to a pointer, the first pointer contains the address of the second pointer, which
points to the location that contains the actual value as shown below.

A variable that is a pointer to a pointer must be declared as such. This is done
by placing an additional asterisk in front of its name. For example, following is
the declaration to declare a pointer to a pointer of type int:

int **var;
When a target value is indirectly pointed to by a pointer to a pointer, accessing
that value requires that the asterisk operator be applied twice, as is shown
below in the example:

#include <iostream>
using namespace std;
int main ()
{
int var;
int *ptr;
int **pptr;
var = 3000;          // take the address of var
ptr = &var;          // take the address of ptr using address of operator &
pptr = &ptr;      // take the value using pptr
cout << “Value of var :” << var << endl;  
cout << “Value available at *ptr :” << *ptr << endl;
cout << “Value available at **pptr :” << **pptr << endl;
return 0;
}
When the above code is compiled and executed, it produces the following result:

Value of var :3000
Value available at *ptr :3000
Value available at **pptr :3000

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