copy constructor clarification

[Rob]

I've just started writing managed C++ (VS 2005 Beta 2) and I really have not
read a whole lot about the differences between managed and unmanaged C++.

Using the class wizard, I can create a managed class defined like:
ref class MyClass {
public
MyClass(void);
~MyClas(void);
};

I'd like to know whether I should add copy and assignment constructors. The
standard syntax of
MyClass(const MyClass&);
MyClass& operator=(const MyClass&);
doesn't work. (compiler error C3699). Do I replace & with ^ ? I would think
that there's times when the default copy constructor will be insufficient.
Part of my confusion stems from my inability to understand the difference
between new and gcnew. When would I want to use one as opposed to the other?

Thanks for any pointers (no pun intended).

[Kapil Khosla [MSFT]]

--
Kapil Khosla, Visual C++ Team
This posting is provided AS IS with no warranties, and confers no rights
"Rob" wrote:

I've just started writing managed C++ (VS 2005 Beta 2) and I really have not
read a whole lot about the differences between managed and unmanaged C++.

Using the class wizard, I can create a managed class defined like:
ref class MyClass {
public
MyClass(void);
~MyClas(void);
};

I'd like to know whether I should add copy and assignment constructors. The
standard syntax of
MyClass(const MyClass&);
MyClass& operator=(const MyClass&);
doesn't work. (compiler error C3699). Do I replace & with ^ ?
The equivalent code would be

ref class MyClass {
public:
MyClass(void);
~MyClass(void);
MyClass(MyClass %);
MyClass% operator=(const MyClass%);
};

Think of the operator equivalence for definitions like this:
& = %
* = ^

Dereferencing a ^ is still done with *, though.

I would think that there's times when the default copy constructor will be insufficient.
Part of my confusion stems from my inability to understand the difference
between new and gcnew.
When would I want to use one as opposed to the other?
You would use new to allocate memory for a native object on the native heap
and gcnew to allocate memory for a manged object on the managed heap. You
can read more on gcnew on
http://msdn2.microsoft.com/library/t...us,vs.80).aspx

Thanks,
Kapil
Thanks for any pointers (no pun intended).

[Ioannis Vranos]

Rob wrote:

I've just started writing managed C++ (VS 2005 Beta 2)
It is not "managed extensions" but C++/CLI.

and I really have not
read a whole lot about the differences between managed and unmanaged C++.

Using the class wizard, I can create a managed class defined like:
ref class MyClass {
public
MyClass(void);
~MyClas(void);
};

I'd like to know whether I should add copy and assignment constructors. The
standard syntax of
MyClass(const MyClass&);
MyClass& operator=(const MyClass&);
doesn't work. (compiler error C3699). Do I replace & with ^ ?

Tracking references are denoted by % and work for both managed and native types. Also you
can define assignment operator like this, but this will work only for C++, and if you use
that type in another language you will have problems.
The managed assignment operator (that is for managed types only) is defined in C++/CLI as
a static member function with two arguments.
You may download the latest C++/CLI draft (currently 1.12) from here:

http://www.plumhall.com/ecma/index.html
I would think
that there's times when the default copy constructor will be insufficient.
Part of my confusion stems from my inability to understand the difference
between new and gcnew. When would I want to use one as opposed to the other?

Thanks for any pointers (no pun intended).

You may check this:

http://www23.brinkster.com/noicys/cppcli.htm

[Rob]

Question below...

"Ioannis Vranos" wrote:

Rob wrote:

I'd like to know whether I should add copy and assignment constructors. The
standard syntax of
MyClass(const MyClass&);
MyClass& operator=(const MyClass&);
doesn't work. (compiler error C3699). Do I replace & with ^ ?

Tracking references are denoted by % and work for both managed and native types. Also you
can define assignment operator like this, but this will work only for C++, and if you use
that type in another language you will have problems.
The managed assignment operator (that is for managed types only) is defined in C++/CLI as
a static member function with two arguments.

So are you saying that I shouldn't define it as
MyClass% operator=(const MyClass%);
because of language interoperabilit y problems but rather as what? Is this it?
void operator=(MyCla ss%, const MyClass%); ?

I will take a look at the 300 page C++/CLI spec, but I feel that Microsoft's
documentation on managed code development in C++ could be a little clearer.

Thanks.

You may download the latest C++/CLI draft (currently 1.12) from here:

http://www.plumhall.com/ecma/index.html

[Ioannis Vranos]

Rob wrote:

So are you saying that I shouldn't define it as
MyClass% operator=(const MyClass%);
because of language interoperabilit y problems but rather as what? Is this it?
void operator=(MyCla ss%, const MyClass%); ?

Well yes, if you intend to share your code with other languages (e.g. making a managed
dll). Otherwise it is OK.
I will take a look at the 300 page C++/CLI spec, but I feel that Microsoft's
documentation on managed code development in C++ could be a little clearer.

Well, the Microsoft documentation is MSDN, and they have the VS 2005 Beta on line. Check
the following on this subject:
http://msdn2.microsoft.com/library/d...us,vs.80).aspx
and what is new in general:

http://msdn2.microsoft.com/library/x...us,vs.80).aspx

[Ioannis Vranos]

Rob wrote:

So are you saying that I shouldn't define it as
MyClass% operator=(const MyClass%);
because of language interoperabilit y problems but rather as what? Is this it?
void operator=(MyCla ss%, const MyClass%); ?

ref class MyClass
{
// ...

public:
static MyClass %operator=(cons t MyClass %x, const MyClass %y)
{
// ...
}

// ...
};
is an example. They are similar to global function ISO C++ operator overloading. You can
also define them as global functions and member functions as usual, but these will not be
accessible from the other managed languages.

[Rob]

Thanks. I was well aware of msdn2.microsoft .com/library, but didn't have the
specific links you provided. I had searched that site for "copy constructor"
but did not find anything. I hadn't yet tried searching for operator=,
although that page wouldn't have shown up for that either. :-)

"Ioannis Vranos" wrote:

Rob wrote:

So are you saying that I shouldn't define it as
MyClass% operator=(const MyClass%);
because of language interoperabilit y problems but rather as what? Is this it?
void operator=(MyCla ss%, const MyClass%); ?

Well yes, if you intend to share your code with other languages (e.g. making a managed
dll). Otherwise it is OK.

I will take a look at the 300 page C++/CLI spec, but I feel that Microsoft's
documentation on managed code development in C++ could be a little clearer.

Well, the Microsoft documentation is MSDN, and they have the VS 2005 Beta on line. Check
the following on this subject:
http://msdn2.microsoft.com/library/d...us,vs.80).aspx
and what is new in general:

http://msdn2.microsoft.com/library/x...us,vs.80).aspx

[Rob]

Actually, operator= cannot be a static member as you show below. You get
compiler error C2581 followed by C2801. In fact, binary operators such as
operator= cannot have two parameters. The first parameter is implied. See
C2804.

So, I will go back to Kapil's suggested syntax.

-Rob

"Ioannis Vranos" wrote:

Rob wrote:

So are you saying that I shouldn't define it as
MyClass% operator=(const MyClass%);
because of language interoperabilit y problems but rather as what? Is this it?
void operator=(MyCla ss%, const MyClass%); ?

ref class MyClass
{
// ...

public:
static MyClass %operator=(cons t MyClass %x, const MyClass %y)
{
// ...
}

// ...
};
is an example. They are similar to global function ISO C++ operator overloading. You can
also define them as global functions and member functions as usual, but these will not be
accessible from the other managed languages.

[Ioannis Vranos]

Rob wrote:

Actually, operator= cannot be a static member as you show below. You get
compiler error C2581 followed by C2801. In fact, binary operators such as
operator= cannot have two parameters. The first parameter is implied. See
C2804.

C++/CLI is currently in draft and has not been finished yet. VC++ 2005 is still under
development and not everything has not been implemented yet. *So far* in the draft
C++/CLI, things are as I have described them.

Beta 1 did not support other things, but now does. And the current Beta also does not
support all current C++/CLI draft features.

Do not rely completely on the current Beta to learn C++/CLI. Let's wait C++/CLI to be
finished itself first. :-)

[Rob]

That's fine from the perspective of learning C++/CLI, but I'm trying to use
VS 2005 Beta 2 to write code and I would've thought that correct assignment
operator syntax would've been put into the compiler kind of early on.

Otherwise, what's the "workaround "? Only create ref classes that can be
shallow copied? I posted a separate question on the syntax I need since
making the changes as suggested by Kapil leaves a problem with member
property assignment.

-Rob

"Ioannis Vranos" wrote:

Rob wrote:

Actually, operator= cannot be a static member as you show below. You get
compiler error C2581 followed by C2801. In fact, binary operators such as
operator= cannot have two parameters. The first parameter is implied. See
C2804.

C++/CLI is currently in draft and has not been finished yet. VC++ 2005 is still under
development and not everything has not been implemented yet. *So far* in the draft
C++/CLI, things are as I have described them.

Beta 1 did not support other things, but now does. And the current Beta also does not
support all current C++/CLI draft features.

Do not rely completely on the current Beta to learn C++/CLI. Let's wait C++/CLI to be
finished itself first. :-)