C Pointer to Pointer

1. What is a Pointer to Pointer?

A pointer to pointer points to a pointer variable, which in turn points to another variable.
It’s like two levels of indirection:

Syntax:

data_type → type of variable being pointed to
** → indicates double pointer

2. Example: Basic Pointer to Pointer

#include <stdio.h>

int main() {
int num = 50; // normal variable
int *ptr = &num; // pointer to num
int **pptr = &ptr; // pointer to pointer

printf("Value of num = %d\n", num);
printf("Address of num = %p\n", &num);
printf("Value of ptr (address of num) = %p\n", ptr);
printf("Value pointed by ptr = %d\n", *ptr);
printf("Address of ptr = %p\n", &ptr);
printf("Value of pptr (address of ptr) = %p\n", pptr);
printf("Value pointed by pptr (value of ptr) = %p\n", *pptr);
printf("Value pointed twice by pptr = %d\n", **pptr);

return 0;
}

#include <stdio.h>

int main() {

int num = 50; // normal variable

int *ptr = &num; // pointer to num

int **pptr = &ptr; // pointer to pointer

printf("Value of num = %d\n", num);

printf("Address of num = %p\n", &num);

printf("Value of ptr (address of num) = %p\n", ptr);

printf("Value pointed by ptr = %d\n", *ptr);

printf("Address of ptr = %p\n", &ptr);

printf("Value of pptr (address of ptr) = %p\n", pptr);

printf("Value pointed by pptr (value of ptr) = %p\n", *pptr);

printf("Value pointed twice by pptr = %d\n", **pptr);

return 0;

}

Output (example):

*pptr → value of ptr (address of num)
**pptr → value of num

3. Pointer to Pointer with Functions

Pointers to pointers are used for modifying pointers inside functions.

#include <stdio.h>

void updatePointer(int **ptr) {
static int x = 100; // must be static to persist
*ptr = &x; // change the pointer to point to x
}

int main() {
int num = 50;
int *ptr = &num;

printf("Before: *ptr = %d\n", *ptr);

updatePointer(&ptr);

printf("After: *ptr = %d\n", *ptr);

return 0;
}

#include <stdio.h>

void updatePointer(int **ptr) {

static int x = 100; // must be static to persist

*ptr = &x; // change the pointer to point to x

}

int main() {

int num = 50;

int *ptr = &num;

printf("Before: *ptr = %d\n", *ptr);

updatePointer(&ptr);

printf("After: *ptr = %d\n", *ptr);

return 0;

}

Output:

Passing &ptr allows the function to modify the pointer itself, not just the value it points to.

4. Pointer to Pointer with Arrays of Pointers

Useful for arrays of strings:

Output:

ptr is a pointer to the first string pointer.

5. Key Points About Pointer to Pointer

Declared using data_type **ptr2;.
*ptr2 gives the value of the first pointer.
**ptr2 gives the value of the actual variable.
Useful for:
- Modifying pointers inside functions
- Arrays of strings
- Dynamic memory allocation (double pointers for 2D arrays)

C Pointer to Pointer

1. What is a Pointer to Pointer?

2. Example: Basic Pointer to Pointer

3. Pointer to Pointer with Functions

4. Pointer to Pointer with Arrays of Pointers

5. Key Points About Pointer to Pointer

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C Pointer to Pointer

1. What is a Pointer to Pointer?

2. Example: Basic Pointer to Pointer

3. Pointer to Pointer with Functions

4. Pointer to Pointer with Arrays of Pointers

5. Key Points About Pointer to Pointer

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