pointeur de pointeur en language c

A pointer to a pointer, also known as a double pointer, is a concept in the C programming language that allows you to indirectly access and modify the value of a pointer variable. It is denoted by the use of two asterisks ().

To understand the concept of a pointer to a pointer, let's break it down into steps:

Step 1: Declare a pointer variable First, you need to declare a pointer variable. This is done by using the asterisk () symbol before the variable name. For example, int ptr; declares a pointer variable named ptr that can hold the memory address of an integer variable.

Step 2: Assign a memory address to the pointer variable Next, you assign a memory address to the pointer variable. This is done by using the ampersand (&) operator followed by the variable name. For example, int num = 10; and then ptr = # assigns the memory address of num to the pointer variable ptr.

Step 3: Declare a pointer to a pointer Now, to declare a pointer to a pointer, you need to use two asterisks () before the variable name. For example, int ptr_to_ptr; declares a pointer to a pointer variable named ptr_to_ptr.

Step 4: Assign the address of the pointer variable to the pointer to a pointer variable To assign the address of the pointer variable to the pointer to a pointer variable, you use the ampersand (&) operator before the pointer variable name. For example, ptr_to_ptr = &ptr; assigns the address of ptr to ptr_to_ptr.

Step 5: Access and modify the value using the pointer to a pointer Finally, you can access and modify the value of the original variable using the pointer to a pointer. To access the value, you use the asterisk () operator before the pointer to a pointer variable name. For example, *ptr_to_ptr gives you the value of num.

Here's a complete example to illustrate the steps:

#include <stdio.h>

int main() {
  int num = 10;
  int *ptr;
  int ptr_to_ptr;

  ptr = &num;
  ptr_to_ptr = &ptr;

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

  return 0;
}

In this example, ptr_to_ptr is a pointer to a pointer to an integer. It first points to ptr, which in turn points to num. By dereferencing ptr_to_ptr twice (ptr_to_ptr), we can access the value of num indirectly.

I hope this explanation helps! Let me know if you have any further questions.