Difference between Reference and Pointer in C++

In C++, reference and pointer seem to be similar, but some differences exist between them. A reference is a variable that is another name of the existing variable, while the pointer is a variable that stores the address of another variable.

In this article, we will discuss the difference between reference and pointer in C++. Before discussing their differences, we must know about references and pointers in C++.

What is a Reference in C++?

A reference is defined using the ampersand (&) symbol. An alias for an existing variable in C++ is a reference variable, which gives access to the same memory location with a different name. When we once initialized a reference to a variable, it cannot be modified to refer to another variable.

C++ Reference Example

Let us take an example to illustrate the reference in C++.

Output:

The value of 'i' variable is :8

Explanation:

In this example, we have created a reference variable, i.e., 'a' for 'i' variable. After creating a reference variable, we can access the value of 'i' with the help of 'a' variable.

What is a Pointer in C++?

A pointer is a variable that contains the address of another variable. It can be dereferenced with the help of (*) operator to access the memory location to which the pointer points. It can be utilized with any data type, such as arrays, basic data types, and user-defined types, including classes and structures.

C++ Pointer Example

Let us take an example to illustrate the pointer in C++.

Output:

First number: 13
Second number: 9
Addition: 22

Explanation:

In this example, we store the addresses of two integers x and y in pointers ptr1 and ptr2 and then access their values using dereferencing (*ptr1 and *ptr2) to calculate their sum. Finally, it prints the original values and the result of the addition.

Key differences between Reference and Pointer

There are several key differences between reference and pointer in C++. Some main differences are as follows:

Definition

In C++, a reference variable is another name for an already existing variable. It is mainly used in 'pass by reference' where the reference variable is passed as a parameter to the function, and the function to which this variable is passed works on the original copy of the variable. On the other hand, a Pointer is a variable that stores the address of another variable. It makes the programming easier as it holds the memory address of some variable.

Declaration

In C++, a reference variable can be declared by adding a '&' symbol before a variable. If this symbol is used in the expression, it will be treated as an address operator. On the other hand, before using a pointer variable, we should declare a pointer variable, and this variable is created by adding a '*' operator before a variable.

Reassignment

In C++, we cannot reassign the reference variable. On the other hand, the pointers can be re-assigned. It is useful when we are working with the data structures, such as linked lists, trees, etc.

Memory Address

In the case of reference, both the reference and actual variable refer to the same address. A reference always refers to the same variable it was initialized with. It cannot be changed to refer to another variable.

Reference Example:

Output:

The address of 'a' variable is : 0x7fff078e7e44 
The address of 'i' variable is : 0x7fff078e7e4

Explanation:

The above output shows that both the reference variable and the actual variable have the same address.

In the case of pointers, both the pointer variable and the actual variable will have different memory addresses.

Pointer Example

Output:

The memory address of p variable is :0x7ffef9ea3db0
The memory address of k variable is :0x7ffef9ea3dac

NULL Value

In C++, we cannot assign the NULL value to the reference variable. On the other hand, the pointer variable can be assigned with a NULL value.

Indirection

In C++, pointers can have a pointer to pointer, which offers more than one level of indirection.

Pointer Example:

Output:

The value of q is : 0x7fffc17a95f4

Explanation:

In this example, the pointer 'p' is pointing to variable 'a' while 'q' is a double pointer that is pointing to 'p'. Therefore, we can say that the value of 'p' would be the address of the 'a' variable, and the value of the 'q' variable would be the address of the 'p' variable.

On the other hand, references only contain one level of indirection in C++.

Reference Example:

Output:

main.cpp: In function 'int main()':
main.cpp:18:10: error: cannot bind 'int' lvalue to 'int&&'
int &&q=p;  // Only valid with std::move

Arithmetic Operations

In C++, arithmetic operations can be applied to the pointers named "Pointer Arithmetic". On the other hand, arithmetic operations cannot be applied to the references. There is no word, i.e., Reference Arithmetic exists in C++.

Difference between Reference and Pointer in Tabular Form

Here, we will discuss several differences between references and pointers in tabular form in C++.

Conclusion

In conclusion, C++ references and pointers both provide several methods to access and manipulate data indirectly, but they can be served for different purposes. References are easy to understand and simple, which makes them suitable for parameter passing and aliasing.

On the other hand, pointers provide greater flexibility, which enables null values, reassignment, and dynamic memory handling. We can choose these methods based on our requirements. References are suitable when simplicity and safety are required, and pointers when more control and dynamic behaviour are required.