Question

Please explain each parameter passing method, when to use it, and code a function prototype example.

a. Pass-by-rvalue

b. Pass-by-const-lvalue-reference

Answer 1

To understand the parameters, it is needed to understand the rvalue and lvalue first:

• rvalue :

It refers to an expression that is used to identify an object that is temporary or whose value is not associated with any stored object.

• lvalue :

It refers to an expression that is used to identify an object that is temporary or whose value is not associated with any stored object.

Parameter passing methods:

1. Pass-by-rvalue: This method of parameter passing is used when we need to express disposable objects in our program. Only one copy of parameter is there and all the modifications that are applied on the passed value will get reflected in the region that is called.

2. Pass-by-const-lvalue: This method of parameter passing is used when we need to express disposable objects in our program. The passed value will not get reflected in the region that is called. The advantages of pass by constant reference is that, it gives much more flexibility and is memory efficient.

Function prototype using an example:

Example: An example to state the use of the given parameter passing methods is given as follows:

void prototypeFunction( const & a);     // passing by L-value reference or const reference

void prototypeFunction ( int && x);      // passing by r-value reference

int main()

{

Int a = 5, b = 10, c = 15;

Int &x = a;

Const int& creference = a + b;         // const reference attached to rvalue

// Int &Lreference = a + b;

Int && x2 = a + b;                            // rvalue reference attached to rvalue

Int arr[50];

prototypeFunction (a);                                   

prototypeFunction (arr[5]);

prototypeFunction (a + b);

prototypeFunction (100);

}

Void prototypeFunction ( const int &a )

{

Cout<< “ function is passed by l-value reference \n”);

}

Void prototypeFunction ( int && a)

{

Cout<< “ function is passed by r-value reference \n”);

}