C++ Dereference Operator

👉 C++ Dereference Operator (*)

In C++, the dereference operator (*) is used to access or modify the value stored at the memory address held by a pointer.

🔹 1. What Does Dereferencing Mean?

  • A pointer stores an address

  • Dereferencing means getting the value at that address

🔹 2. Basic Dereference Example

int x = 10;
int *p = &x;

cout << p; // prints address of x
cout << *p; // prints value of x (10)

🔹 3. Dereference to Modify Value

int x = 5;
int *p = &x;

*p = 20;

cout << x; // Output: 20

➡ Value changed using dereference.

🔹 4. Dereference in Functions

void update(int *n) {
*n = 100;
}

int x = 10;
update(&x);

cout << x; // 100

🔹 5. Dereference with Arrays

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

cout << *p; // 10
cout << *(p + 1); // 20
cout << *(p + 2); // 30

🔹 6. Dereference a Pointer to Pointer

int x = 10;
int *p = &x;
int **pp = &p;

cout << **pp; // 10

🔹 7. Dereference vs Declaration (* Meaning)

int *p; // * → pointer declaration
*p = 10; // * → dereference

👉 Same symbol, different meanings based on context.

🔹 8. Dereference with const

Pointer to Constant

const int x = 10;
const int *p = &x;

// *p = 20; ❌ not allowed

Constant Pointer

int x = 10;
int *const p = &x;

*p = 20; // allowed

❌ Common Mistakes

❌ Dereferencing Uninitialized Pointer

int *p;
cout << *p; // undefined behavior

✔ Correct

int x = 10;
int *p = &x;

❌ Dereferencing Null Pointer

int *p = nullptr;
cout << *p; // crash

🔁 Dereference vs Address-of

OperatorMeaning
&xAddress of x
*pValue at address p

📌 Summary

  • Dereference operator * accesses value at address

  • Used with pointers and pointer-to-pointer

  • Can read or modify data

  • Must never dereference NULL or uninitialized pointers

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