C++ References

In C++, a reference is an alias for another variable. Once a reference is initialized with a variable, it can be used interchangeably with that variable. References are commonly used for function arguments to avoid copying large data and to allow modifications to the original variable.

Syntax

data_type &reference_name = variable_name;

Where:

References must be initialized when declared.
References cannot be made to null or reassigned to reference another variable.
Passing by reference allows functions to modify the original variable and avoids copying large data.

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data_type – Type of the variable being referenced.
&reference_name – Declares a reference using the ampersand &.

Example: Basic Reference

#include <iostream>
using namespace std;

int main() {

    int num = 10;
    int &ref = num; // Reference to num

    cout << "Original num: " << num << endl;
    cout << "Reference ref: " << ref << endl;

    // Modifying value through reference
    ref = 20;
    cout << "Modified num: " << num << endl;

    return 0;
}

Output

Original num: 10
Reference ref: 10
Modified num: 20

Example: Reference as Function Parameter

#include <iostream>
using namespace std;

// Function to double a number using reference
void doubleValue(int &x) {
    x = x * 2;
}

int main() {

    int num = 15;
    cout << "Before: " << num << endl;

    doubleValue(num); // Pass by reference
    cout << "After: " << num << endl;

    return 0;
}

Output

Before: 15
After: 30

Important Notes

References must be initialized when declared.
References cannot be made to null or reassigned to reference another variable.
Passing by reference allows functions to modify the original variable and avoids copying large data.

Next Topic

Next, learn about C++ Classes and Objects.