C++ Pointers: Memory Addressing, Dereferencing Mechanics & Modern nullptr

A Pointer is a variable that stores the physical hexadecimal memory address of another variable in RAM. Pointers give C++ programmers unparalleled power to directly inspect and manipulate hardware memory with maximum execution speed.

Figure 5: Memory Mechanics: Direct Variable Aliasing vs Indirect Pointer Addressing

The Two Fundamental Pointer Operators

1. Address-of Operator (&): Retrieves the physical RAM address of a variable.
2. Dereference Operator (*): Accesses or modifies the value stored at the address pointed to by the pointer.

#include <iostream>

int main() {
    int target = 42;
    int* ptr = &target; // ptr stores the memory address of target

    std::cout << "Value of target:          " << target << "\n";       // 42
    std::cout << "Memory address (&target): " << &target << "\n";      // e.g., 0x7ffd98
    std::cout << "Address stored in ptr:    " << ptr << "\n";          // 0x7ffd98
    std::cout << "Dereferenced value (*ptr):" << *ptr << "\n";         // 42

    // Modifying the value via pointer dereference:
    *ptr = 100;
    std::cout << "New value of target:      " << target << "\n";       // 100!

    return 0;
}

Pointer Arithmetic

When you increment a pointer (ptr++), C++ does NOT add 1 byte. Instead, it advances the pointer by sizeof(T) bytes, matching the size of the underlying data type:

int arr[] = {10, 20, 30};
int* p = arr;

std::cout << *p << "\n";       // 10
p++; // Moves forward by sizeof(int) = 4 bytes!
std::cout << *p << "\n";       // 20