Const makes all the difference. Why?

[seppel]

class T{int i; public: T(int i):i(i){}};

int main(){
T& a1(0); //C2440
const T& a2(0);
}

[ThangDo]

"_"
ur problem is?
ur question is?
what does that piece of code do?

"_"

[seppel]

Defined are two references a1 and a2. The difference between a1 and a2 is only const. Without const in main error C2440 is pulled. Why?

[DSLq5Di1]

http://stackoverflow.com/questions/2088259/literal-initialization-for-const-references

[happykiller]

Const is unchangable...

[seppel]

Using the constructor
T::T(int i)
via the call
a1(0)
an object of type T or const T was created.
The literal was copied via the copy constructor of build-in type int into the data-member i.
The const or non-const reference a1 or a2 can then be initialized with this newly created non-literal object.
Still cant see why T& a1(0) is not working.

[seppel]

Somebody?

[seppel]

Anybody?

[Disch]

Still cant see why T& a1(0) is not working.

A T& by itself is not an object. It merely references another object by a different name. In order to have a T&, you must also have a T (ie: a non-reference object).

Consider this:

T obj(0);  // OK
T& ref(obj); // OK 

Here, 'ref' and 'obj' are different names for the same object: 'obj'. If you change 'ref', you are also changing 'obj'.

With that in mind... think about what you're trying to do here:

T& a1(0);

This code makes no sense. To what object is a1 referring to? There's no T here. That's why the compiler complains.