What is a reference?
- C++ course
- Beginner
- Lesson 71/116
- 5 min
Learn that a reference is an alias for a variable.
What is a reference?
A reference is an alias for an existing variable. Once a reference is declared, every operation through it affects the original variable, because both refer to the same memory location.
Example: int x = 10; int& r = x;. Here r is an alias for x. Writing r = 20; also makes x become 20. Unlike a pointer, a reference cannot be re-bound to another variable after its first binding; it is fixed at initialization.
Reference versus pointer
A reference is like a pointer but safer. A pointer is a separate variable and can be nullptr; a reference is bound to a variable at initialization and cannot be null.
The syntax is also cleaner: you write r, not *p. But a reference is less flexible; it cannot be re-bound. So when you want 'an alias for a variable', choose a reference; when you want 'an independent address', choose a pointer.
Practice Modify through a reference
Declare int x = 10;. Bind a reference with int& r = x;. Write r = 20;. Finally print x with std::cout.
Starter code
#include <iostream>
int main() {
// Declare x
// Bind r as a reference to x
// Assign to r
// Print x
return 0;
}Sample solution
#include <iostream>
int main() {
int x = 10;
int& r = x;
r = 20;
std::cout << x << "\n";
return 0;
}Expected output
20
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is a reference?
- A memory address
- A kind of pointer
- A new variable type
- An alias for a variable Correct answer
Explanation: A reference is an alias for an existing variable.
2 Reference declaration
int x = 10;
int____ r = x;int x = 10;
int& r = x;Explanation: int& r = x; makes r a reference to x.
3 Match each expression to its meaning
| Term | Meaning |
|---|---|
int& r |
Reference declaration |
int x = 10 |
Variable declaration |
r = 20 |
Reference assignment |
std::cout << x |