Can a name of a object be name of any other class?

[vishnupriya.sureshbabu]

consider i have two classes A and B. Is it wrong declaring a object of
type A with name B?
class A{}
class B{}
A B;
Why is it wrong?

 

[Jim Langston]

consider i have two classes A and B. Is it wrong declaring a object of
type A with name B?
class A{}
class B{}
A B;
Why is it wrong?

Suprisingly, this compiles, and in my limited test actually works. I would
say it's wrong, but I can't say why. This actually compiles and produces
the output "10" which I would not expect.

Not suprisingly, you can't say
A A;
however. But if you could say A B; why couldn't you say A A;?

#include <iostream>
#include <string>

class A {
public:
int X;
friend std:stream& operator<< (std:stream& os, const A& Instance );
};

std:stream& operator<< (std:stream& os, const A& Instance )
{
os << Instance.X;
return os;
}

class B { };

int main()
{
A B;
B.X = 10;

std::cout << B << std::endl;

std::string wait;
std::cin >> wait;

return 0;
}

 

[vishnupriya.sureshbabu]

It will not give an error but it will not allow to instantiate an
object of type B. It does not identify the declaration of calss B. Can
anyone explain?

 

[Kai-Uwe Bux]

consider i have two classes A and B. Is it wrong declaring a object of
type A with name B?
class A{}
class B{}
A B;
Why is it wrong?

It is not.

[3.3/4]

Given a set of declarations in a single declarative region, each of which
specifies the same unqualified name,
? they shall all refer to the same entity, or all refer to functions and
function templates; or
? exactly one declaration shall declare a class name or enumeration name
that is not a typedef name and the other declarations shall all refer to
the same object or enumerator, or all refer to functions and function
templates; in this case the class name or enumeration name is hidden.


So what you are doing is not illegal, but you are hiding class B. As a
matter of coding style, however, I would stay away from such things.


Best

Kai-Uwe Bux

 

[Jim Langston]

It will not give an error but it will not allow to instantiate an
object of type B. It does not identify the declaration of calss B. Can
anyone explain?

Oh yeah! Now it makes sense. You are simply hiding the class B by the
definition of a variable B.

Same as this.

#include <iostream>
int i = 10;

int main()
{
int i = 20;
std::cout << i << std::endl; // prints 20, the global i is hidden
}

it's just in your case B is a class definition and an instance of another
class instead of both being ints. Makes sense now.

 

[vishnupriya.sureshbabu]

Though the instance of the class is overriding the class definition. So
if the class is redefined after the object is instantiated it should
work right? But it doesnt seem to.
Class A{}
Class B{}
A B;
Class B{}
B C;
It does not recognise class B which is used for instantiating C

 

[Boris Kolpackov]

Though the instance of the class is overriding the class definition. So
if the class is redefined after the object is instantiated it should
work right? But it doesnt seem to.
Class A{}
Class B{}
A B;
Class B{}
B C;
It does not recognise class B which is used for instantiating C

Since B-variable hides B-type, all unqualified references to B now
resolve to B-variable. To get to the type you will need to qualify
it:

class B C;

hth,
-boris

 

[deepak.babu]

A very related link -
http://blog.devstone.com/Aaron/archive/2005/02/24/205.aspx

 

[Stuart Golodetz]

A very related link -
http://blog.devstone.com/Aaron/archive/2005/02/24/205.aspx

How's it in any way related? It's not even to do with C++ as far as I can
see...

Cheers,
Stu

 

[Boris Kolpackov]

A very related link -
http://blog.devstone.com/Aaron/archive/2005/02/24/205.aspx

I fail to see how it is related. Even if we disregard the fact that it
talks about C#, there is nothing remotely related to re-using names
of types and instances.

-boris

 

[Jim Langston]

I fail to see how it is related. Even if we disregard the fact that it
talks about C#, there is nothing remotely related to re-using names
of types and instances.

I think he replied to the wrong message. There is another message thread a
few down that he also replied with this same message wehre it actually was
related.