References

A reference variable is an alias for another object. It is created using the & sign.

Two things to note:

• Anything done to the reference also happens to the original.
• Aliases cannot be changed to alias something else.

Syntax

int &alias = varname;

Pass-By-Reference

In C++, pass-by-reference refers to passing parameters to a function by using references.

It allows the ability to:

• Modify the value of the function arguments.
• Avoid making copies of a variable/object for performance reasons.

void swap_num(int &i, int &j) {
  int temp = i;
  i = j;
  j = temp;
}

int main() {
  int a = 100;
  int b = 200;

  swap_num(a, b);

  std::cout << "A is " << a << "\n";
  std::cout << "B is " << b << "\n";
}

const Reference

In C++, pass-by-reference with const can be used for a function where the parameter(s) won’t change inside the function.

This saves the computational cost of making a copy of the argument.

int triple(int const &i) {
  return i * 3;
}