The object that you use to initialize a reference must be of the same type as the reference, or it must be of a type that is convertible to the reference type. If you initialize a reference to a constant using an object that requires conversion, a temporary object is created. In the following example, a temporary object of type float is created:
int i;
const float& f = i; // reference to a constant float
When you initialize a reference with an object, you bind that reference to that object.
Attempting to initialize a nonconstant reference with an object that requires a conversion is an error.
Once a reference has been initialized, it cannot be modified to refer to another object. For example:
int num1 = 10;
int num2 = 20;
int &RefOne = num1; // valid
int &RefOne = num2; // error, two definitions of RefOne
RefOne = num2; // assign num2 to num1
int &RefTwo; // error, uninitialized reference
int &RefTwo = num2; // valid
Note that the initialization of a reference is not the same as an assignment to a reference. Initialization operates on the actual reference by initializing the reference with the object it is an alias for. Assignment operates through the reference on the object referred to.
A reference can be declared without an initializer:
You cannot have references to any of the following: