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Matthias Hofmann
Guest
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 Posted: Wed Jun 15, 2005 10:23 am Post subject: Accessing private member - bug or feature? |
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Hello!
I have stumbled into something that really confuses me. The following code
compiles without any problems under both VC++ 6 and 7:
class A
{
// Private nested class.
class B
{
public:
void g() {}
};
public:
// Return object of private class.
B f() { return B(); }
};
int main()
{
A().f().g(); // Accessing private member.
return 0;
}
Note that B is a private nested class of class A. I expected the code to be
rejected, however I can call A::B::g(). Is this legal? Of course one might
interpret the declaration of A::f() returning an object of type B as an
agreement to bypass the private declaration.
I also found out that VC++ 6 does not reject the following either, while
VC++ 7 does:
int main()
{
A::B();
return 0;
}
I did not know that there were such severe problems in VC++ 6...
--
Matthias Hofmann
Anvil-Soft, CEO
http://www.anvil-soft.com - The Creators of Klomanager
http://www.anvil-soft.de - Die Macher des Klomanagers
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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diginux
Guest
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| Posted: Wed Jun 15, 2005 10:41 pm Post subject: Re: Accessing private member - bug or feature? |
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I think this would be legal, since A().f().g() really is just returning
g() from an "instance" of B(). With that said, the code is very
confusing, I hope you aren't planning on adopting it for anything :)
| Quote: | class A
{
// Private nested class.
class B
{
public:
void g() {}
};
public:
// Return object of private class.
B f() { return B(); }
};
int main()
{
A().f().g(); // Accessing private member.
return 0;
}
|
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Ben Hutchings
Guest
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| Posted: Wed Jun 15, 2005 10:51 pm Post subject: Re: Accessing private member - bug or feature? |
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Matthias Hofmann <hofmann (AT) anvil-soft (DOT) com> wrote:
| Quote: | Hello!
I have stumbled into something that really confuses me. The following code
compiles without any problems under both VC++ 6 and 7:
class A
{
// Private nested class.
class B
{
public:
void g() {}
};
public:
// Return object of private class.
B f() { return B(); }
};
int main()
{
A().f().g(); // Accessing private member.
return 0;
}
Note that B is a private nested class of class A. I expected the code to be
rejected, however I can call A::B::g(). Is this legal?
|
Yes. Accessibility checks apply to individual member name lookups and
not to the complete qualified names for the members they find. Since
the lookup that finds member A::B is done within A::f(), it is legal,
and since the lookup that finds A::B::g() does not name A::B, it is
also legal.
| Quote: | Of course one might
interpret the declaration of A::f() returning an object of type B as an
agreement to bypass the private declaration.
|
Exactly.
| Quote: | I also found out that VC++ 6 does not reject the following either, while
VC++ 7 does:
int main()
{
A::B();
return 0;
}
I did not know that there were such severe problems in VC++ 6...
|
That *is* a bug in VC++ 6.
--
Ben Hutchings
Having problems with C++ templates? Your questions may be answered by
<http://womble.decadentplace.org.uk/c++/template-faq.html>.
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Greg
Guest
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| Posted: Wed Jun 15, 2005 11:06 pm Post subject: Re: Accessing private member - bug or feature? |
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Matthias Hofmann wrote:
| Quote: | Hello!
I have stumbled into something that really confuses me. The following code
compiles without any problems under both VC++ 6 and 7:
class A
{
// Private nested class.
class B
{
public:
void g() {}
};
public:
// Return object of private class.
B f() { return B(); }
};
int main()
{
A().f().g(); // Accessing private member.
return 0;
}
Note that B is a private nested class of class A. I expected the code to be
rejected, however I can call A::B::g(). Is this legal? Of course one might
interpret the declaration of A::f() returning an object of type B as an
agreement to bypass the private declaration.
I also found out that VC++ 6 does not reject the following either, while
VC++ 7 does:
int main()
{
A::B();
return 0;
}
I did not know that there were such severe problems in VC++ 6...
|
The statement:
A().f().g();
is invoking three public methods so there is no access violation.
Whether class B's declaration is private or not is irrelevant.
Greg
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]
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