What is a pointer in C++?

In C++, a pointer is a variable that stores the memory address of another variable. Instead of holding the actual data value, a pointer holds the address where that value is located in memory. Pointers are a powerful feature in C++ that enable efficient handling of arrays, dynamic memory allocation, and object manipulation.

Basic Syntax of a Pointer:

• To declare a pointer, use the * symbol along with the data type of the variable the pointer will point to.

int* ptr; // A pointer to an integer

Key Concepts of Pointers:

1. Pointer Declaration: When declaring a pointer, you specify the type of data the pointer will point to (e.g., int*, char*).

   int x = 10;
   int* ptr = &x;  // Pointer to x, holding the memory address of x

2. Dereferencing a Pointer: The * operator is used to access the value stored at the memory address the pointer points to. This is called dereferencing the pointer.

   cout << *ptr;  // Outputs the value of x (10)

3. Pointer Arithmetic: Pointers can be incremented or decremented to traverse through arrays, as each increment moves the pointer to the next element of the array based on the data type size.

   int arr[] = {10, 20, 30};
   int* ptr = arr;
   ptr++;  // Moves to the next element in the array (arr[1])

4. Null Pointer: A null pointer is a pointer that does not point to any memory address. You can assign nullptr to a pointer to indicate that it is not pointing to any valid memory location.

   int* ptr = nullptr;  // Null pointer, points to nothing

5. Pointer to Pointer: You can also have pointers that point to other pointers. These are called pointer-to-pointer.

   int x = 10;
   int* ptr = &x;
   int** ptr2 = &ptr;  // Pointer to pointer

Example of Pointers in C++:

#include <iostream>
using namespace std;

int main() {
    int var = 20;
    int* ptr = &var;  // Pointer holding the address of var

    cout << "Value of var: " << var << endl;
    cout << "Address of var: " << ptr << endl;
    cout << "Value at the address: " << *ptr << endl;  // Dereferencing the pointer

    return 0;
}

Uses of Pointers:

• Dynamic Memory Allocation: Pointers are essential for allocating memory dynamically using new and delete.
• Arrays and Strings: Pointers make handling arrays and strings easier and more efficient.
• Function Parameters: Pointers allow functions to modify the actual variables passed to them, enabling pass-by-reference.
• Data Structures: Pointers are crucial for implementing data structures like linked lists, trees, and graphs.

Sources:

• GeeksforGeeks: Pointers in C++
• Programiz: C++ Pointers