Lesson 5	Call-by-reference
Objective	Examine C++'s implementation of call-by-reference

C++ Call by Reference

The chief use of reference declarations is in formal parameter lists. This allows C++ to have call-by-reference arguments directly, a feature not available in C.

Example

Let uslook at an example program that uses reference declarations and call-by-reference.
The function greater exchanges two values if the first is greater than the second.

int greater(int& a, int& b){
 if (a > b) {   //exchange
  int temp = a;
  a = b;
  b = temp;
  return (1);
 }
 else
  return (0);
 }

If i and j are two int variables, then

greater(i, j)

uses the reference to i and the reference to j to exchange, if necessary, their two values. In traditional C, this operation must be accomplished using pointers and dereferencing.

Call-by-reference and const

When function arguments are to remain unmodified, it can be efficient and correct to pass them const call-by-reference. This is the case for types that are structures.

struct large_size{
  int mem[N];
  //...other stuff
};

void print(const large_size& s){
  //since s will not be modified
  //avoid call-by-value copying
  //...
}