Dereference Operator in C: What It Is and How It Works

In C, the * symbol is called the dereference operator. It is used to access or modify the value stored at the memory address held by a pointer variable.

How It Works

The dereference operator * lets you reach inside a pointer to get or change the actual value it points to. Think of a pointer as a street address written on a piece of paper. The dereference operator is like going to that address and opening the door to see what's inside.

When you declare a pointer, it holds the memory address of a variable, not the variable's value itself. Using *pointer means you are asking: "Give me the value stored at this address." This is essential for working with dynamic data and for efficient memory use.

Example

This example shows how to declare a pointer, assign it the address of a variable, and then use the dereference operator to access and change the variable's value.

c

#include <stdio.h>

int main() {
    int number = 10;
    int *ptr = &number;  // ptr holds the address of number

    printf("Original value: %d\n", number);

    *ptr = 20;  // change value at the address ptr points to

    printf("New value: %d\n", number);
    return 0;
}

Output

Original value: 10
New value: 20

When to Use

Use the dereference operator when you want to work directly with the value stored at a memory address, especially when using pointers. This is common in:

• Modifying variables inside functions via pointers.
• Working with dynamic memory allocation.
• Accessing elements in data structures like linked lists or trees.

It helps write efficient programs by avoiding copying large amounts of data and enabling flexible data manipulation.

Key Points

• The dereference operator * accesses the value at a pointer's address.
• It is different from the address-of operator &, which gets the address of a variable.
• Using * on a pointer lets you read or change the original variable.
• Always ensure the pointer points to a valid memory location before dereferencing to avoid errors.

Key Takeaways

The dereference operator (*) accesses the value stored at a pointer's memory address.

It allows reading or modifying the original variable through its pointer.

Use it when working with pointers to manipulate data efficiently.

Always ensure pointers are valid before dereferencing to prevent crashes.