Reference to reference is not allowed in ISO C++ 2003 standard, but why it is allowed by compilers?

Question

According to ISO C++ 2003 standard section 8.3.2

"references to references are not allowed"

But I have tried following code in Visual C++ and Ideone, and both compilers are running this code successfully.

Ideone GCC C++4.3.2

int main() 
{
    int i=2;
    int &ref_i=i;
    int &ref_ref_i=ref_i; // should be an error according to c++ 2003 standard

    cout<<i<<endl<<ref_i<<endl<<ref_ref_i;  
    return 0;
}

I am really confused after looking at this behavior of compilers; can someone explain this?

Answer 1

You do not create a reference-to-reference in your code.

It is just another int&, i.e. both are references to an int

(T.C. shows an example of an illegal C++03 reference to reference)

---

The C++11 Standard section § 8.3.2 explicitly shows this by an example (disallowing references of references, of course, did not change between C++03 and C++11, but reference collapsing is new in C++11) :

If a typedef-name (7.1.3 , 14.1) or a decltype-specifier (7.1.6.2) denotes a type TR that is a reference to a type T, an attempt to create the type “lvalue reference to cv TR” creates the type “lvalue reference to T”, while an attempt to create the type “rvalue reference to cv TR” creates the type TR.

int i;
typedef int& LRI;
typedef int&& RRI; 

LRI& r1 = i; // r1 has the type int&
const LRI& r2 = i; // r2 has the type int& 
const LRI&& r3 = i; // r3 has the type int&