CppReference.md

Reference

A function argument can be passed by copy, reference or pointer.

void f(T t); //t is a copy of the value passed
void f(T &t); //t is the value passed
void f(T* t); //t is a pointer to the value passed passed

When a function argument is passed by reference, the function can modify the original variable.

 

#include <cassert>

void swap(int& x, int& y)
{
  const int temp{x};
  x = y;
  y = temp;
}

int main()
{
  int value1{1};
  int value2{2};
  swap(value1, value2);
  assert(value1 == 2);
  assert(value2 == 1);
}

Advice

• Prefer const reference arguments to plain reference arguments [1]
• Use const reference to express immutability in interfaces [2]
• Prefer references to pointers as arguments, except where "no object" is a reasonable option [3]
• Use pass-by-const-reference to pass large values that you don't need to modify, use pass-by-non-const-reference only if you have to [5]
• Only return references to dynamic allocated data, data that existed before the function was called, or static data [6]
• Do not keep references of temporary expressions [7]

const double& r = std::real(std::complex(3, 7)); //Bad [7]

• Polymorphic types must always be passed by reference or (smart) pointer [8]

References

1. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 7.8. Advice. page 199: '[9] Prefer const reference arguments to plain reference arguments'
2. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 7.8. Advice. page 199: '[13] Use const pointers and const references to express immutability in interfaces'
3. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 7.8. Advice. page 199: '[14] Prefer references to pointers as arguments, except where "no object" is a reasonable option'
4. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 12.7. Advice. page 341: '[8] Use pass-by-const-reference to pass large values that you don't need to modify'
5. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 12.7. Advice. page 341: '[12] Use pass-by-non-const-reference only if you have to'
6. Gottschling, Peter. Discovering Modern C++: An Intensive Course for Scientists, Engineers, and Programmers. Addison-Wesley Professional, 2015. Chapter 1.8.6: 'Only return pointers and references to dynamic allocated data, data that existed before the function was called, or static data'
7. Gottschling, Peter. Discovering Modern C++: An Intensive Course for Scientists, Engineers, and Programmers. Addison-Wesley Professional, 2015. Chapter 2.6.1: 'Do not keep references of temporary expressions!'
8. Gottschling, Peter. Discovering Modern C++: An Intensive Course for Scientists, Engineers, and Programmers. Addison-Wesley Professional, 2015. Chapter 6.1.3: 'Polymorphic types must always be passed by reference or (smart) pointer!'