R-Value references in C++ 11

Firstly, We have to understand the L-values and r-values which are the properties of expression.

All l-values have assigned the memory address whereas r-values are temporary values (they die at the end of the expression they are in).

e.g.

int x = 3;                              

Here x is l-value and 3 is r-value because x has memory address whereas memory of 3 will die in next statement.

‘l-value reference’ refer to l-value whereas ‘r-value reference’ refer to r-value.

l-value references are declared with one ampersand whereas r-value references with two ampersands.

e.g.

        int a = 3;
	int & b = a;		//b is l-value reference
	int && c = 3;		//c is r-value reference
	int &d = 3;		//We get an error:” invalid initialization of non-const reference of                                            ’                                         
                                //type int& from an rvalue of type int”

Note that const & can bind to r-value e.g. const int &e = 5;

Functions can also be overloaded on the basis of l-value reference and r-value reference.

e.g.

int fun(int & a) {cout <<”lvalue ref”;}
int fun(int &&a) {cout<<”rvalue ref”;}