C Pointer to Pointer

Explore the concept of C Pointer to Pointer in this comprehensive guide. Understanding pointers is essential for effective programming in C, and pointers to pointers offer advanced techniques for managing memory and data structures. This article delves into the syntax, usage, and practical applications of C Pointer to Pointer, providing valuable insights for both novice and experienced developers. Enhance your coding skills by mastering this critical aspect of C programming.

1. What is a C Pointer to Pointer?

In C 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 C 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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