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Hi,

I have a doubt regarding using references.
Please look at the below code. I am using VC++ 6.0

int &i = 10; // Compilation error

error C2440: 'initializing' : cannot convert from 'const int' to 'int &'
A reference that is not to 'const' cannot be bound to a non-lvalue

Assume that "Test" is a class
Test &t = Test(); // No compilation error

Why for built-in types assigning non-const reference with a non-lvalue is
giving error and for the
User defined type it is not giving any error?

Thanks
VSP

VSP wrote:

> I have a doubt regarding using references.
> Please look at the below code. I am using VC++ 6.0
>
> int &i = 10; // Compilation error
>
> error C2440: 'initializing' : cannot convert from 'const int' to 'int &'
> A reference that is not to 'const' cannot be bound to a non-lvalue
>
> Assume that "Test" is a class
> Test &t = Test(); // No compilation error
>
> Why for built-in types assigning non-const reference with a non-lvalue is
> giving error and for the
> User defined type it is not giving any error?

According to the standard, you should see an error in both cases.
Apparently, your compiler is broken. Try:

struct Test {};

int main ( void ) {
Test & t = Test();
}


at: http://www.comeaucomputing.com/tryitout/



Best

Kai-Uwe Bux

> I have a doubt regarding using references.
> Please look at the below code. I am using VC++ 6.0
>
> int &i = 10; // Compilation error
>
> error C2440: 'initializing' : cannot convert from 'const int' to 'int &'
> A reference that is not to 'const' cannot be bound to a non-lvalue
>
> Assume that "Test" is a class
> Test &t = Test(); // No compilation error
>
> Why for built-in types assigning non-const reference with a non-lvalue is
> giving error and for the
> User defined type it is not giving any error?

Your compiler is broken.
Try your sample on Comeau online -
http://www.comeaucomputing.com/tryitout
m

Kai-Uwe Bux wrote:
> VSP wrote:
>
> > I have a doubt regarding using references.
> > Please look at the below code. I am using VC++ 6.0
> >
> > int &i = 10; // Compilation error
> >
> > error C2440: 'initializing' : cannot convert from 'const int' to 'int &'
> > A reference that is not to 'const' cannot be bound to a non-lvalue
> >
> > Assume that "Test" is a class
> > Test &t = Test(); // No compilation error
> >
> > Why for built-in types assigning non-const reference with a non-lvalue is
> > giving error and for the
> > User defined type it is not giving any error?
>
> According to the standard, you should see an error in both cases.
> Apparently, your compiler is broken. Try:
>
> struct Test {};
>
> int main ( void ) {
> Test & t = Test();
> }
>
>
> at: http://www.comeaucomputing.com/tryitout/
>
>
>
> Best
>
> Kai-Uwe Bux

Let us look at this from a different angle, before dismissing it. Note
that, at "Test()" an object is in fact created, within the same scope
as the reference to it. So, within that scope, t can indeed reach the
object. This is not in voilation of object-oriented view, though it may
violate the standard.
However, C++ takes the C built-in types as is. Then, the literal 10 is
not an object (not an l-value for C). There is nothing to point to
because a literal for a built-in is only available during compilation
unless it is assigned to an object (of its type).

Regards,

http://www.zhmicro.com
http://distributed-software.blogspot.com
http://groups-beta.google.com/group/...Z?lnk=la&hl=en

Zorro wrote:

> Let us look at this from a different angle, before dismissing it. Note
> that, at "Test()" an object is in fact created, within the same scope
> as the reference to it. So, within that scope, t can indeed reach the
> object. This is not in voilation of object-oriented view, though it may
> violate the standard.

So you wonder what is the reasoning behind that decision in the standard ?

> However, C++ takes the C built-in types as is. Then, the literal 10 is
> not an object (not an l-value for C). There is nothing to point to
> because a literal for a built-in is only available during compilation
> unless it is assigned to an object (of its type).

But for references to const C++ allows to bind to a literal like that.

int const& i = 10;
(the compiler will create a temporary in the same scope)

It's someway unified that references to const are allowed to temporaries
even to literals like that and it makes programming typeless interfaces (ie
templates) easier.

--
Dizzy
http://dizzy.roedu.net

Dizzy wrote:
> Zorro wrote:
>
> > Let us look at this from a different angle, before dismissing it. Note
> > that, at "Test()" an object is in fact created, within the same scope
> > as the reference to it. So, within that scope, t can indeed reach the
> > object. This is not in voilation of object-oriented view, though it may
> > violate the standard.
>
> So you wonder what is the reasoning behind that decision in the standard ?
>
> > However, C++ takes the C built-in types as is. Then, the literal 10 is
> > not an object (not an l-value for C). There is nothing to point to
> > because a literal for a built-in is only available during compilation
> > unless it is assigned to an object (of its type).
>
> But for references to const C++ allows to bind to a literal like that.
>
> int const& i = 10;
> (the compiler will create a temporary in the same scope)
>
> It's someway unified that references to const are allowed to temporaries
> even to literals like that and it makes programming typeless interfaces (ie
> templates) easier.
>
> --
> Dizzy
> http://dizzy.roedu.net

The compiler error already indicated that it could do it for const. How
is const related to what I said?
I am aware of C++ templates accepting literals like "10", instead of
types. That is because C++ template instantiation is done the same way
C macros are, i.e. text editing. I am not objecting to this, just
saying how it works, and that is the way one should accept it.

Please note that I was explaining why VC++ did not generate error for
Test(). That is because, Test() is an object (after elaboration). There
is no const involved in my response.

Thanks for your comment, though.
Regards.