C++の一般参照

Reference to const
We can bind a reference to const to a nonconst object, a literal, or a more general expression:

    int i = 42;				
	const int &r1 = i;		//bind a const int& to a plain int object
	const int &r2 = 42;		//ok.r1 is a reference to const
	const int &r3 = r1 * 2;         //ok.r3 is a reference to const
	int &r4 = i * 1;		//error.r4 is a plain,nonconst reference

    double dval= 30;
	const int &rDval = dval; 
	dval = 42;
	cout << rDval << endl; // print 30

The compiler transforms this code into something like:

    const int temp = dval;
	const int &rDval = temp;

In this case, rDval is bound to a temportary object.