Returning another class' function value

Helper

On 17/02/2013 at 15:55, xxxxxxxx wrote:

Interesting. There's a little bit of everything going on in that example.

I just want to share a class's members upwards to the previous class.
But this thing is also using friend, and shared pointers. And I'm not sure how much part those things are playing in that end goal.
I'll have to study this thing for a while and try to see if I can simplify it with some more simplistic LONG type class member variables and see if I can get the MyData class to share upwards to the previous class.

Thanks,
-ScottA

Helper

On 17/02/2013 at 21:05, xxxxxxxx wrote:

Thanks for the conversation folks.
Over at my end however, it's still not recieving the right String value. Whenever I copy another string over to the functions string, it returns an empty value. See below for what I'm trying to do.
This one works:

  
class MyClass1  
{  
public:  
 String MyString(String temp)  
  {  
      temp = String("Print successful!");  
      return temp;  
  }  
};

But this one doesn't:

  
class MyClass1  
{  
String AnotherString;    // class level String variable.  
public:  
Init(void)  
  {  
      AnotherString = String("This way won't work.");  
  }  
 String MyString(String temp)  
  {  
      // AnotherString (and 'temp') always returns empty when done this way  
      // AnotherString = String("Doesn't work either.");    // uncommenting this line doesn't work either.  
      temp = AnotherString;  
      return temp;  
  }  
};

What's the differene here? Why won't the second way work?
WP.

Helper

On 18/02/2013 at 01:24, xxxxxxxx wrote:

Hi WickedP,

what's the sense of passing a string that is not used at all? Are you calling Init() before MyString() ?
You're also missing the return-type for the Init() method. Also note that a void parameter is
deprecated for C++ and is used in C only.

http://ideone.com/GZeyoY

#include <string>
#include <iostream>
 
class MyClass {
    
    std::string my_string;
    
public:
 
    void Init() {
        my_string = "Hello!";
    }
    
    std::string GetMyString() {
        return my_string;
    }
    
};
 
int main() {
    MyClass obj;
    obj.Init();
    std::cout << obj.GetMyString();
}

ScottA :

The following does not work: http://ideone.com/ASo7LI
The function MyFoo::DoStuff() is not declared since MyFoo is an incomplete type at the point
MyFoo::DoStuff() is used.

#include <string>
#include <iostream>
 
#define PFUNC() do { std::cout << \__FUNCTION\_\_ << "\n"; } while (0)
 
class MyFoo;
 
class MyBar {
    
    MyFoo\* foo;
 
public:
 
    MyBar(MyFoo\* foo) : foo(foo) {
    }
 
    void DoStuff() {
        PFUNC();
**         foo->DoStuff(); // MyFoo is still an incomplete type!**
    }
};
 
class MyFoo {
    
public:
 
    void DoStuff() {
        PFUNC();
    }
};
 
int main() {
    MyFoo foo;
    MyBar bar(&foo);
    
    bar.DoStuff();
}

Implementing MyBar::DoStuff() after MyFoo became a complete type, it
works: http://ideone.com/3G2Xub

#include <string>
#include <iostream>
 
#define PFUNC() do { std::cout << \__FUNCTION\_\_ << "\n"; } while (0)
 
class MyFoo;
 
class MyBar {
    
    MyFoo\* foo;
 
public:
 
    MyBar(MyFoo\* foo) : foo(foo) {
    }
 
    ** void DoStuff();**
};
 
class MyFoo {
    
public:
 
    void DoStuff() {
        PFUNC();
    }
};
 
**void MyBar ::DoStuff() {
    PFUNC();
    foo->DoStuff(); // MyFoo is now a complete type!
}**
 
int main() {
    MyFoo foo;
    MyBar bar(&foo);
    
    bar.DoStuff();
}

If that's not what you mean, and does not solve the problem, could you please post a full
example that you think should compile but doesn't because of the undefined class error?

-Niklas

Helper

On 18/02/2013 at 01:56, xxxxxxxx wrote:

Hi Nik,
just to clarify a few points for you:

Originally posted by xxxxxxxx

what's the sense of passing a string that is not used at all?

the string is used in MyClass1 (which is actually a GeUserArea) but the userarea code is hundreds of lines long so I was a bit reluctant to paste all of that. The example I've been providing above is just a basic translated version of what I have.

Originally posted by xxxxxxxx

Are you calling Init() before MyString() ?

As it's a user area, Init is called first. However the string is being updated/defined in a few other functions so it is in use elsewhere, and is for other purposes.

Originally posted by xxxxxxxx

You're also missing the return-type for the Init() method. Also note that a void parameter is
deprecated for C++ and is used in C only.

My mistake in translating things over. Needless to say the string (and the GeUserArea) all runs as expected, and the string variable is filled well before any call to the "MyString()" function is run. The issue seems to be if you get the function's string value from another variable - the string value (both the function's and the class level variable) are when passed to another class.

Cheers,

WP.

Helper

On 18/02/2013 at 02:07, xxxxxxxx wrote:

Originally posted by xxxxxxxx

Sure.Here's a small example:

class MyTag;                <-- In raw C++ this is how you tell the compiler to go get the MyTag class   
                                Problem: This works fine in raw C++. But not when doing it inside of a C4D plugin.   
 
class MyDialog : public GeDialog{   
    public:        MyTag tag;           <--- Complier error: Undefined class!!?   
        GeDialog Overrides   
        Blah, blah, etc..   
  };   
 
class MyTag : public TagData{   
    public:        MyDialog dlg;         <--- MyDialog has been seen by the compiler and works fine   
                                   Note: This works fine in both raw C++ and in C4D plugins   
        TagData Overrides   
        Blah, blah, etc..   
 };

Originally posted by xxxxxxxx

this shouldn't work in a "raw C++" environment, either.

That's a normal forward declaration, and it works. I use it all the time.
To clarify, there is nothing like "CINEMA 4D C++". It's all the same. Standard compiler, standard language, just some custom classes and structs.
No difference in language behavior whatsoever.

Helper

On 18/02/2013 at 03:31, xxxxxxxx wrote:

Hi Jack,

the behaviour with the forward declaring seems to be different, as I get the same compiler error as Scott when forward declaring like that in a C4D plugin.

WP.

Helper

On 18/02/2013 at 04:07, xxxxxxxx wrote:

Originally posted by xxxxxxxx

Hi Jack,

the behaviour with the forward declaring seems to be different, as I get the same compiler error as Scott when forward declaring like that in a C4D plugin.

WP.

"In C++, classes can be forward-declared if you only need to use the pointer-to-that-class type (since all object pointers are the same size, and this is what the compiler cares about)."

Can't use forwards declation with

MyTag tag;

It's just C++, guys. Nothing funny going on here at all.

Helper

On 18/02/2013 at 04:29, xxxxxxxx wrote:

Yes, that's right. The problem you get is usually because the compiler did not parse the classes definition
at the point you want to access a member in the current translation unit. When you forward-declare a class
from a header that does not define the class, you must at least include the header defining the class in the
implementation file so the compiler knows about its definition when the class is used.

-N

Helper

On 18/02/2013 at 07:50, xxxxxxxx wrote:

Originally posted by xxxxxxxx

That's a normal forward declaration, and it works. I use it all the time.
To clarify, there is nothing like "CINEMA 4D C++". It's all the same. Standard compiler, standard language, just some custom classes and structs.
No difference in language behavior whatsoever.

Can you post a working example of bottom up class sharing then?
Fused is correct about the pointer. I posted my example from memory. And I forgot to use a pointer to the bottom class's prototype in my example. It's been a while since I tried doing this and forgot about the pointer.
But even if I do use a pointer to the bottom class's prototype. I still get an undefined class error when I try to actually use that pointer in my code.

Again.
In Raw C++ it's very common to do a bottom up type of sharing of a class to it's previous class.
But in C4D plugins it's not something I can do at all. And apparently other people are having the same problem.
We need to see a working example of bottom up class sharing.

-ScottA

Helper

On 18/02/2013 at 08:13, xxxxxxxx wrote:

Like this one ?

  
    
    
    class SecondOne;
     
    //=====================================================================================================================
    class FirstOne
    {
    	friend SecondOne;
    public:
    	FirstOne(SecondOne &ref) 
    		: m_first_string("first_string")
    		, m_ref_to_second(ref)
    	{}
     
    	void Print();
    	void PrintSecond(SecondOne &ref);
    private:
    	String m_first_string;
     
    	SecondOne	&m_ref_to_second;
    };
     
    //=====================================================================================================================
    class SecondOne
    {
    	friend FirstOne;
    public:
    	SecondOne() 
    		: m_second_string("second_string")
    		, m_first(*this) 
    	{}
     
    	void Print() { GePrint(m_first.m_first_string); }
    	void PrintFirst(FirstOne &ref);
     
    private:
    	String m_second_string;
     
    	FirstOne	m_first;
    };
     
    // ----------------------------------------------------------------------------------------------------
    void SecondOne::PrintFirst( FirstOne &ref )
    {
    	GePrint(ref.m_first_string);
    }
    // ----------------------------------------------------------------------------------------------------
    void FirstOne::PrintSecond(SecondOne &ref)
    {
    	GePrint(ref.m_second_string);
    }
    // ----------------------------------------------------------------------------------------------------
    void FirstOne::Print()
    {
    	GePrint(m_ref_to_second.m_second_string);
    }

Helper

On 18/02/2013 at 08:27, xxxxxxxx wrote:

Doh!
I was going to edit my post to say that we need to see a working example of the bottom up class sharing. Using the existing SDK classes (tag, GeDialog, object, etc..). Not custom hand made classes.
But you were too quick Remo.

I was wondering if maybe using generic custom classes to test this on isn't a good way to test this. Because custom classes don't have header files or inheritance in them the same as the built-in SDK classes.
So I'm wondering if the reason I'm getting undefined class errors is because of the way the built-in SDK classes are set up with their .h files and inheritance structures.

Do you happen to know if that code will also work for the built-in SDK classes Remo?
Have you tried this using two of the existing SDK classes?

-ScottA

Helper

On 18/02/2013 at 08:55, xxxxxxxx wrote:

Hm, do you mean ObjectData, TagData ?
The short answer is it is not allowed and make no sense.

C4D own all this stuff.
Of course you can still use pointers to it.
BaseObject [URL-REMOVED]*obj= BaseObject[URL-REMOVED]::Alloc(MY_PLUGIN_ID);

An the ObjectData is then inside of BaseObject.[URL-REMOVED]
This can be acceded using GetNodeData().

[URL-REMOVED] @maxon: This section contained a non-resolving link which has been removed.

Helper

On 18/02/2013 at 09:50, xxxxxxxx wrote:

Then I'm right back to square one. Not being able to up share my tag's class members with a previous GeDialog's class.
Which is why I say that working in these C4D plugins is sometimes different than working in Raw C++.

Based on your post. It sounds like sharing two SDK classes is better done by allocation. And not by trying to break down the OOP class structure between them.
Since this has nothing to do with the OP. I better stop posting here and return control back to WickedP.
I apologize for hijacking your thread WP.

Thanks for the information guys. I'm always learning new things from you guys.
-ScottA

Helper

On 18/02/2013 at 10:54, xxxxxxxx wrote:

Originally posted by xxxxxxxx

Then I'm right back to square one. Not being able to up share my tag's class members with a previous GeDialog's class.Which is why I say that working in these C4D plugins is sometimes different than working in Raw C++. Based
on your post. It sounds like sharing two SDK classes is better done by
allocation. And not by trying to break down the OOP class structure
between them.Since this has nothing to do with the OP. I better stop posting here and return control back to WickedP.I apologize for hijacking your thread WP.Thanks for the information guys. I'm always learning new things from you guys.-ScottA

You can definitely do that (not easily across different plugins DLLs tho).

What you are missing is a cast.

And you also have to call GetNodeData() on the tag. You plugin tag is not derived from C4DAtom (like BaseTag) but from NodeData.
The NodeData is attached to the GeListNode (which is derived from C4DAtom ).

To safely get the pointer to your plugins node data from a BaseTag:

  
BaseTag* yourTag = BaseTag::Alloc(YOUR_PLUGIN_ID);//(where ever you may be getting it from, allocate?)   
  
YourPluginClass* yourPlugin = NULL;   
  
if(yourTag != NULL && yourTag->GetType() == YOUR_PLUGIN_ID)   
{   
    yourPlugin = static_cast<YourPluginClass*>(yourTag->GetNodeData());   
}

edit: fixed some stuff

Helper

On 18/02/2013 at 11:13, xxxxxxxx wrote:

Regarding forwards declaration of classes. You can only forwards declare them when all you do after forwards declaration is declaring a pointer. As soon as you access it, you need to include the header file.

Examples...

Wrong:

  
  
class BaseTag;   
  
class class1   
{   
public:   
    BaseTag* tag; // forwards declaration is fine, since we are just declaring the a pinter.   
  
    void doStuff()   
    {   
        LONG type = tag->GetType(); // Compiler error. "Undefined class BaseTag". When using the pointer the compiler needs to know more about the class.   
    }   
};

Right:

  
  
#include <c4d.h> // Inlcudes "c4d_basetag.h"   
  
class class1   
{   
public:   
    BaseTag* tag;   
  
    void doStuff()   
    {   
        LONG type = tag->GetType(); // No compiler error. The compiler knows the class.   
    }   
};

Helper

On 18/02/2013 at 12:58, xxxxxxxx wrote:

Thanks fused.
But I'm not sure how to write your casting code. I don't know what "YourPluginClass" supposed to be standing for?

Here's an example of a dialog class with a tag class below it. And trying to share one of the tag's class members with the GeDialog class above it:

  
#define DIALOG_PLUGIN_ID 1000001   //The GeDialog plugin's ID  
#define TAG_PLUGIN_ID     1000002   //The Tag plugin's ID  
  
  
//-------- The GeDialog plugin --------------------//  
//-------------------------------------------------//  
class MyDialog : public GeDialog  
{  
  public:  
      MyDialog();          
      BaseTag* tag;  
      void doStuff()  
      {  
          LONG type = tag->GetType();  
          GePrint(LongToString(type));  
      }  
  
  
      //GeDialog Overrides  
      Bool CreateLayout();  
      Bool InitValues();  
      Bool Command(LONG id, const BaseContainer& data);  
      Bool CoreMessage(LONG id, const BaseContainer& data);  
  
};  
  
MyDialog::MyDialog()  //The GeDialog's constructor  
{  
  GeDialog();  
  
  tag = BaseTag::Alloc(TAG_PLUGIN_ID);  
  MyDialog* MyDialog = NULL;  
  
  if(tag != NULL && tag->GetType() == TAG_PLUGIN_ID)  
  {  
      //yourPlugin = static_cast<YourPluginClass*>(tag->GetNodeData()); //<----Not sure how to write this..What does "YourPluginClass" stand for?  
      MyDialog = static_cast<MyDialog*>(tag->GetNodeData());  //<-------wrong!  
      MyDialog = static_cast<GeDialog*>(tag->GetNodeData());    //<-------wrong!  
  }  
}  
... etc.  
  
//-------- The tag plugin -------------------------//  
//-------------------------------------------------//  
class StorageTag : public TagData  
{  
  public:  
      static NodeData* Alloc()  
      {  
          return gNew StorageTag;  
      }  
  
      LONG imagecount;         //<---I want to share this class member so I can use it inside the MyDialog class  
  
  
      //Overrides  
      StorageTag();  
      Bool Init(GeListNode* node);  
      void Free(GeListNode* node);  
      Bool Read(GeListNode* node, HyperFile* file, LONG level);  
      Bool Write(GeListNode* node, HyperFile* file);  
      Bool Message(GeListNode* node, LONG id, void* msgData);  
};  
...etc.

-ScottA

Helper

On 18/02/2013 at 13:14, xxxxxxxx wrote:

YourPluginClass stands for the class derived from NodeData (from which TagData, ObjectData, etc are dervied). In your example that would be StorageTag.

     tag = BaseTag::Alloc(TAG_PLUGIN_ID);   
    StorageTag* MyTag = NULL;   
  
    if(tag != NULL && tag->GetType() == TAG_PLUGIN_ID)   
    {   
        MyTag = static_cast<StorageTag*>(tag->GetNodeData());   
    }

Helper

On 18/02/2013 at 13:33, xxxxxxxx wrote:

Ok thanks.
Fixed that. But still running into undeclared errors.

MyDialog::MyDialog()  
{  
  GeDialog();  
  
  tag = BaseTag::Alloc(TAG_PLUGIN_ID);  
  StorageTag* MyTag = NULL;          //<------------ undeclared identifier :-(  
  
  if(tag != NULL && tag->GetType() == TAG_PLUGIN_ID)  
  {  
      MyTag = static_cast<StorageTag*>(tag->GetNodeData());  
  }  
}

-ScottA

Helper

On 18/02/2013 at 13:42, xxxxxxxx wrote:

You've missed the forward-declaration, then.

Helper

On 18/02/2013 at 13:47, xxxxxxxx wrote:

Oh, you need to declare StorageTag first and MyDialog.

So:

#define DIALOG_PLUGIN_ID 1000001   //The GeDialog plugin's ID   
#define TAG_PLUGIN_ID     1000002   //The Tag plugin's ID   
  
  
//-------- The tag plugin -------------------------//   
//-------------------------------------------------//   
class StorageTag : public TagData   
{   
    ...   
};   
  
//-------- The GeDialog plugin --------------------//   
//-------------------------------------------------//   
class MyDialog : public GeDialog   
{   
   ...   
  
};

The other option would be to move each classes declaration/definition into it's own h/cpp files and have them the MyDialog file include/forwards declare the StorageTag (don't forget "#pragma once"/include guards).