Implementation of Pointers in C++

 Basic Pointer Operations

Storing address in a pointer

int x = 5;

int* p = &x;

 

Printing address and value

cout << "Address of x: " << p << endl;

cout << "Value at p: " << *p << endl;

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Pointer Dereferencing

Dereference = Access value at the stored address

int x = 20;

int* p = &x;

 

cout << *p;   // prints 20

 

Changing value via pointer:

*p = 100;   // modifies x

cout << x;  // prints 100

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Pointers and Arrays

Arrays and pointers are closely related. Pointer store first element address of array.

int arr[3] = {10, 20, 30};

int* p = arr;     // arr = &arr[0]

 

Access elements through pointer:

cout << *p;     // 10

cout << *(p+1); // 20

cout << *(p+2); // 30

Pointer arithmetic works in multiples of data type size.

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Pointer Arithmetic

Operation	Meaning
p++	Move to next element
p--	Move to previous element
p + n	Move forward n elements
p - n	Move backward n elements

 

Example:

int arr[] = {2,4,6,8};

int* p = arr;

 

cout << *p;     // 2

p++;

cout << *p;     // 4

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Pointers to Pointers (Double Pointer)

A pointer storing the address of another pointer.

int x = 10;

int* p = &x;

int** q = &p;

 

Access values:

cout << x;     // 10

cout << *p;    // 10

cout << **q;   // 10

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Pointers and Functions

Pass-by-pointer

Used to modify values inside a function.

void update(int* p) {

    *p = *p + 10;

}

 

int main() {

    int x = 5;

    update(&x);

    cout << x;     // 15

}

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Dynamic Memory Allocation

Allocate memory:

int* p = new int;   // allocate 4 bytes

*p = 10;

 

Allocate array:

int* arr = new int[5];

 

Free memory:

delete p;       // free 1 variable

delete[] arr;   // free array

 

delete

Avoids memory leaks.

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Void Pointers

Can store address of any data type, but cannot be directly dereferenced.

void* p;

int x = 10;

p = &x;

Must cast:

cout << *(int*)p;

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Null Pointer

Pointer that points to nothing.

int* p = nullptr;

Used for safety checks.

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Wild Pointer

Uninitialized pointer (dangerous!).

int* p;   // wild

Fix:

p = nullptr;

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Dangling Pointer

Pointer pointing to deleted or out-of-scope memory.

Example:

int* p = new int(5);

delete p;

cout << *p;    // DANGEROUS

Fix:

p = nullptr;

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Complete Practical Example

#include <iostream>

using namespace std;

 

int main() {

    int x = 50;

    int* p = &x;

 

    cout << "Value of x: " << x << endl;

    cout << "Address of x: " << &x << endl;

    cout << "Pointer p stores: " << p << endl;

    cout << "Value at p: " << *p << endl;

 

    *p = 200;

    cout << "New value of x: " << x << endl;

 

    int arr[3] = {1, 2, 3};

    int* q = arr;

 

    cout << *(q+0) << " " << *(q+1) << " " << *(q+2) << endl;

 

    return 0;

}

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