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);

}

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].

References

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'
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'
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'
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'
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'

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(C++) Reference

References