Re: Why does this compile with VC++?

From:

"Duane Hebert" <spoo@flarn2.com>

Newsgroups:

microsoft.public.vc.language

Date:

Tue, 27 Feb 2007 21:00:12 -0500

Message-ID:

<Oo9rvwtWHHA.5060@TK2MSFTNGP06.phx.gbl>

"Defect Architect" <DefectArchitect@discussions.microsoft.com> wrote in
message news:03DC3017-A427-4D46-9109-351A9886866A@microsoft.com...

"Defect Architect" wrote:

"Victor Bazarov" wrote:

Defect Architect wrote:

class A
{
public:

A(int)
{
}

private:

A(const A &);
A &operator=(const A &);
};

A foo()
{
return A(0);
}

void bar()
{
A a = foo();
}

Even though the compiler may optimize out the call to the copy
constructor, it should still respect the fact that it is declared
private.

From the C++ standard:

"Even when the creation of the temporary object is avoided, all the
semantic restrictions must be respected as if the temporary object
was created."

1>------ Build started: Project: test, Configuration: Release
Win32 ------
1>Compiling...
1>Test.cpp
1>.\Test.cpp(17) : error C2248: 'A::A' : cannot access private member
declared in class 'A'
1> .\Test.cpp(11) : see declaration of 'A::A'
1> .\Test.cpp(2) : see declaration of 'A'
1>.\Test.cpp(17) : error C2248: 'A::A' : cannot access private member
declared in class 'A'
1> .\Test.cpp(11) : see declaration of 'A::A'
1> .\Test.cpp(2) : see declaration of 'A'
1> while checking that elided copy-constructor 'A::A(const A &)'
is
callable
1> .\Test.cpp(11) : see declaration of 'A::A'
1> when converting from 'A' to 'const A &'
1>.\Test.cpp(22) : error C2248: 'A::A' : cannot access private member
declared in class 'A'
1> .\Test.cpp(11) : see declaration of 'A::A'
1> .\Test.cpp(2) : see declaration of 'A'
1>.\Test.cpp(22) : error C2248: 'A::A' : cannot access private member
declared in class 'A'
1> .\Test.cpp(11) : see declaration of 'A::A'
1> .\Test.cpp(2) : see declaration of 'A'
1> while checking that elided copy-constructor 'A::A(const A &)'
is
callable
1> .\Test.cpp(11) : see declaration of 'A::A'
1> when converting from 'A' to 'const A &'
1>test - 4 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped
==========

Not sure what you're complaining about.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

Sorry. That did not accurately reproduce my scenario. What about this:

class A
{
public:

  A(int)
  {
  }

private:

  A(const A &);
  A &operator=(const A &);
};

class B : public A
{
public:
  B(int) : A(0)
  {
  }
};

B foo()
{
  return 0;
}

void bar()
{
  B b = foo();
}

Does B have an implicit copy constructor? If so, how does it handle A's
private copy constructor? If it works, why can I not add this line to
bar() ?

B b2 = b;

Thanks!

This does not compile with gcc 4.02.

Borland Turbo C++ generates an error:
[C++ Error] Unit1.cpp(34): E2285 Could not find a match for 'B::B(const B&)'
on the line B b = foo();