In C, a double pointer is a variable that stores the address of a pointer. It is also known as a pointer-to-pointer. Double pointers are useful when you need to modify the value of a pointer itself, not just the value it points to.
Declaring Double Pointer in C:
Here is an example of how to declare a double pointer in C:
int **pptr;
In the above example, pptr is a double pointer to an integer type. It can store the address of a pointer to an integer.
To access the value that the double pointer is pointing to, you need to dereference it twice. Here’s an example:
int *ptr;
int a = 10;
ptr = &a; // pointer to the variable a
pptr = &ptr; // double pointer to the pointer ptr
// Accessing the value of variable a using the double pointer
printf("%d", **pptr); // Output: 10
In the above example, ptr is a pointer to the variable a, and pptr is a double pointer to the pointer ptr. To access the value of a using pptr, we need to dereference pptr twice using the ** operator.
Double pointers are commonly used in data structures like linked lists and trees, where you need to modify the pointers that link the nodes. They can also be used to create dynamic two-dimensional arrays.
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