class instances in C++

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I have an application form named Form1.h. The code for this form is a
namespace (MyNamespace) with two classes in it (Form1 and MyClass). Form1 has
windows designer code and some button event handlers. In those event handlers
I want to reference methods in the MyClass class. I use syntax like this:
double F = MyClass::MyMeth od(x,y);

As soon as I type the second colon I get a full list of all the exposed
methods in MyClass and I sense I going the right way. But, I debug and get
two errors:

1) MyClass is not a class or namespace name
2) MyMethod identifier not found

I am not sure why this happens but I sense its because I need an instance of
MyClass to work with in the class Form1. In VB I create an instance of a
class with the new keywork e.g. MyInstance=new MyClass. How is this done in
C++?

[Ben Voigt]

"Max 1e6" <Ma****@discuss ions.microsoft. comwrote in message
news:36******** *************** ***********@mic rosoft.com...

Yup, putting MyClass first works. However, my form designer dissappears.

Yes, because the form designer doesn't actually understand C++, it just
looks for particular patterns in the file. If you move a block of code into
a different file and make it visible in the first file using #include, the
compiler will see it, but the form designer won't get confused (as much).

>
I get the feeling I just don't understand enough about the project files
and
how they interact.

Thanks

"Ben Voigt" wrote:

>>
"Max 1e6" <Ma****@discuss ions.microsoft. comwrote in message
news:AE******* *************** ************@mi crosoft.com...

OK, so now I have (omitting windows designer code):
#pragma once
namespace WA1 {

using namespace System;
using namespace System::Compone ntModel;
using namespace System::Collect ions;
using namespace System::Windows ::Forms;
using namespace System::Data;
using namespace System::Drawing ;
public ref class Form1 : public System::Windows ::Forms::Form
{
private: System::Void button1_Click(S ystem::Object^ sender,
System::EventAr gs^ e) {
MyClass Instance;

The compiler doesn't know MyClass is a type name, because it hasn't seen
MyClass yet. Move the definition of MyClass ahead of where you use it.
If
you have two mutually interacting classes, this will require that you use
a
forward declaration of each class "class MyClass;" to make it usable as a
parameter and/or return type, and then both class bodies with forward
declarations of member functions, and then bodies of each member
function.
That way everything is available to the compiler before it's used.

double x = 2.0;
double F = Instance.MyMeth od(&x);
}
};

public class MyClass{
double MyMethod(double *x){
return *x*2;
}
};
}

Again, intellisense seems to recognize MyClass and MyMethod bcause as
soon
as I type double F = Instance., MyMethod shows up as a choice. But on
degug
I get:

error C2065: 'MyClass' : undeclared identifier
error C2146: syntax error : missing ';' before identifier 'Instance'
error C2065: 'Instance' : undeclared identifier
error C2228: left of '.MyMethod' must have class/struct/union







"Ben Voigt" wrote:
"Max 1e6" <Ma****@discuss ions.microsoft. comwrote in message
news:1B******* *************** ************@mi crosoft.com...
I have an application form named Form1.h. The code for this form is a
namespace (MyNamespace) with two classes in it (Form1 and MyClass).
Form1
has
windows designer code and some button event handlers. In those event
handlers
I want to reference methods in the MyClass class. I use syntax like
this:
double F = MyClass::MyMeth od(x,y);

As soon as I type the second colon I get a full list of all the
exposed
methods in MyClass and I sense I going the right way. But, I debug
and
get
two errors:

1) MyClass is not a class or namespace name
2) MyMethod identifier not found

I am not sure why this happens but I sense its because I need an
instance
of
MyClass to work with in the class Form1. In VB I create an instance
of
a
class with the new keywork e.g. MyInstance=new MyClass. How is this
done
in
C++?

Does MyClass need to maintain state, in such a way that it would be
worth
keeping track of instances? If no, put the 'static' modifier on your
functions, then your function calls will work as-is.

If yes, then you can do:

MyClass instance;
double F = instance.MyMeth od(x, y);

which establishes an instance that is local to the current scope. If
the
object needs to live longer, we need to know if it is a ref class or a
native C++ class. For native C++:
MyClass* pInstance = new MyClass();
double F = pInstance->MyMethod(x, y);
.... later
delete pInstance;

For .NET ref classes:
MyClass^ pInstance = gcnew MyClass();
double F = pInstance->MyMethod(x, y);
.... no need to delete, garbage collector does the work for you