2007-08-31 |  RatheeshTR  | Viewed: 300  |    1

Pass-by-reference parameters:

        Passing by by reference refers to a method of passing the address of an argument in the calling function to a corresponding parameter in the called function. C onlyIn C, the corresponding parameter in the called function must be declared as a pointer type. C++ only In C++, the corresponding parameter can be declared as any reference type, not just a pointer type.

The following function swap uses reference parameters:

            void swap(int& a,int& b)
            {
                int temp = a;
                a = b;
                b = emp;
            }

Now, swap does have an effect on the arguments in the caller - as it must to be of any use. Thus:

              float x=10, y=20, z=0;
             swap(x, y);
             cout<< x<<", "<< y<< endl;

will result in 20, 10

Notice that the caller need not make any special indication of the reference nature of the arguments - that is all handled by the definition of the function: int& a,int& b.

Thus, void swap(int& a,int& b)
Just to drive the point home, let us examine a naive swap which uses pass-by-value.

        void swapSilly(int a,int b) //naive -- pass by value
             {
                  int temp=a;
                  a=b;
                  b=temp;
        }

Now, swap Silly does NOT have an effect on the arguments in the caller, hence the function has no effect. Thus:

          float x=10, y=20, z=0;
               swapSilly(x, y);
               printf ("%d , %d \n",x,y);

will result in 10, 20

Example program:
1. Swap two numbers