Pointer to Pointer

Pointer to Pointer (Double Pointer) Program in C++

IntermediateTopic: Memory Management Programs
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C++ Pointer to Pointer Program

This program helps you to learn the fundamental structure and syntax of C++ programming.

Try This Code
#include <iostream>
using namespace std;

int main() {
    int num = 10;
    int* ptr = &num;        // Pointer to int
    int** ptrToPtr = &ptr;  // Pointer to pointer
    
    cout << "Value of num: " << num << endl;
    cout << "Address of num: " << &num << endl;
    
    cout << "\nValue of ptr (address of num): " << ptr << endl;
    cout << "Address of ptr: " << &ptr << endl;
    cout << "Value pointed by ptr: " << *ptr << endl;
    
    cout << "\nValue of ptrToPtr (address of ptr): " << ptrToPtr << endl;
    cout << "Address of ptrToPtr: " << &ptrToPtr << endl;
    cout << "Value pointed by ptrToPtr: " << *ptrToPtr << endl;
    cout << "Value pointed by *ptrToPtr: " << **ptrToPtr << endl;
    
    // Modify value using double pointer
    **ptrToPtr = 20;
    cout << "\nAfter modifying through double pointer:" << endl;
    cout << "Value of num: " << num << endl;
    
    return 0;
}
Output
Value of num: 10
Address of num: 0x7fff5fbff6ac

Value of ptr (address of num): 0x7fff5fbff6ac
Address of ptr: 0x7fff5fbff6a0
Value pointed by ptr: 10

Value of ptrToPtr (address of ptr): 0x7fff5fbff6a0
Address of ptrToPtr: 0x7fff5fbff698
Value pointed by ptrToPtr: 0x7fff5fbff6ac
Value pointed by *ptrToPtr: 10

After modifying through double pointer:
Value of num: 20

Understanding Pointer to Pointer

A pointer to pointer (double pointer) stores the address of another pointer. It's declared with

. Double pointers are useful for: 1) Dynamic 2D arrays, 2) Modifying pointer values in functions, 3) Linked lists and trees, 4) Passing pointers by reference. They require two levels of dereferencing (

ptrToPtr).

Let us now understand every line and the components of the above program.

Note: To write and run C++ programs, you need to set up the local environment on your computer. Refer to the complete article Setting up C++ Development Environment. If you do not want to set up the local environment on your computer, you can also use online IDE to write and run your C++ programs.

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