Pointers

Table of Contents

• Introduction
• Pointer to Pointer
• Array of Pointer
• Argument of main Function

Introduction

Pointers in C++ are variables that hold the memory addresses of other variables. They allow you to indirectly access and modify the value stored at those addresses.

• Pointer Declaration:

A pointer is declared by specifying the type of data it will point to, followed by an asterisk (*) and the pointer's name.

Code Example:

File: main.cpp

int *ptr;

• Pointing:

When you assign the address of a variable to a pointer, you are "pointing" the pointer to that variable. You use the address-of operator (&) for this.

Code Example:

File: main.cpp

int x = 10;
int *ptr = &x;

• Dereferencing:

Dereferencing a pointer means accessing the value at the memory address stored in the pointer. You use the dereference operator (*) for this.

Code Example:

File: main.cpp

int y = *ptr;

Pointer to Pointer

• A pointer to pointer is a pointer that stores the address of another pointer rather than storing the address of a variable directly.
• Syntax: type** ptrToPtr;

Code Example:

File: main.cpp

#include <iostream>

void swapPointers(int **x, int **y) {
  int *temp;
  temp = *x;
  *x = *y;
  *y = temp;
}

int main() {
  int a = 23;
  int b = 40;

  int *p1 = &a;
  int *p2 = &b;

  swapPointers(&p1, &p2);

  std::cout << "p1 points to: " << *p1 << "\n";
  std::cout << "p2 points to: " << *p2 << "\n";
}

Array of Pointer

An array of pointers is simply an array whose elements are pointer variables. Useful when you want to store multiple addresses, e.g., addresses of different variables or the starting addresses of multiple strings.

Code Example:

File: main.cpp

#include <iostream>

int main(int argc, char **argv) {
  const char *p[3];
  p[0] = "XYZ";
  p[1] = "KLM";
  p[2] = "ABC";

  std::cout << p[1] << std::endl; // p[1] is pointer to "KLM"
  std::cout << *p[1] << std::endl; // *p1[1] is a pointer to "K"
  std::cout << **p << std::endl; // **p is a pointer to "X"
  std::cout << *(p+1) << std::endl; // *(p+1) is a pointer to "KLM"
}

Arguments of main Function

• argc: The number of command-line arguments (argument count).
• argv: An array of C-style strings (argument vector). Each element in argv is a pointer to a character array representing a command-line argument.

Code Example:

File: main.cpp

#include <iostream>

int main(int argc, char **argv) {
  for (int i = 0; i < argc; i++) {
    std::cout << "Argument " << i << ": " << argv[i] << std::endl;
  }
}

Command Line Interface:

./example.exe cat cow dog

Argument 0: ./example.exe
Argument 1: cat
Argument 2: cow
Argument 3: dog