[SOLVED] Help with Declaration Problem

[xiphirx]

Hello,

I have been programming a class called mapEditor, and alongside of it, a very shitty GUI package. The mapEditor class includes the GUI like so

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#include "xi_window.h"

class mapEditor {
...

in the GUI, I need a pointer to a mapEditor class for a specific component, but the mapEditor class is declared AFTER the GUI, so it spits

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 error C2061: syntax error : identifier 'mapEditor'

The mapEditor needs to have the GUI declared first, and the GUI needs the mapEditor to be declared first. How do I resolve this? Is there something with inheritance I can do to declare a type that would suffice for a mapEditor pointer?

Please don't tell me I'm a jackass and need to rewrite D:

[avansc]

then use forward declaration.

[xiphirx]

then use forward declaration.

So, before I include the GUI things in my mapEditor class header, I put

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class mapEditor;

?

I did this, and now it's complaining about an undefined type 'mapEditor'.

[Ginto8]

then use forward declaration.

So, before I include the GUI things in my mapEditor class header, I put

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class mapEditor;

?

I did this, and now it's complaining about an undefined type 'mapEditor'.

every situation in which GUI or w/e is included, you also need to include the mapEditor definition.

[Falco Girgis]

You should ALWAYS be using class prototypes unless you MUST have the actual class declaration within the header file. If it's a pointer, reference, or passing of a parameter, you don't need to be including the header file.

[Ginto8]

You should ALWAYS be using class prototypes unless you MUST have the actual class declaration within the header file. If it's a pointer, reference, or passing of a parameter, you don't need to be including the header file.

sorry I meant prototype not definition

[xiphirx]

You should ALWAYS be using class prototypes unless you MUST have the actual class declaration within the header file. If it's a pointer, reference, or passing of a parameter, you don't need to be including the header file.

I've never really dealt with class prototypes, so this is a bit confusing...

So say I had the class mapEditor, and another class called otherClass. In otherClass's header, I want to use the class mapEditor, so I would just prototype the class mapEditor?

[MrDeathNote]

You should ALWAYS be using class prototypes unless you MUST have the actual class declaration within the header file. If it's a pointer, reference, or passing of a parameter, you don't need to be including the header file.

I've never really dealt with class prototypes, so this is a bit confusing...

So say I had the class mapEditor, and another class called otherClass. In otherClass's header, I want to use the class mapEditor, so I would just prototype the class mapEditor?

Yip thats pretty much the idea of it.

[xiphirx]

Am I missing something here? I successfully prototyped my mapEditor class, and it recognizes it, but whenever I use one of the pointed to class's methods, the compiler says it's undefined...

So, if you are using forward declaration, you can just store pointers? you cant actually use them? :/

EDIT:

I'm passing the pointer to the mapEditor class as an argument to a function,

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void button::onClick(map * theMap, mapEditor * editor)

later down in the code, this is what causes an error

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editor->newMap(openFileName());

[RyanPridgeon]

Am I missing something here? I successfully prototyped my mapEditor class, and it recognizes it, but whenever I use one of the pointed to class's methods, the compiler says it's undefined...

So, if you are using forward declaration, you can just store pointers? you cant actually use them? :/

Not when they've only been forward-declared. But this doesn't matter. In the header where you're forward declaring, you don't NEED to use them. You can include the entire class definition in the source file where you're actually defining the functions, but just use forward declaration in the header to avoid the include loop.

[xiphirx]

I'm becoming lost...
so I put

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class mapEditor;
#include "mapeditor.h"

?

...

[lotios611]

I think it should be

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#include "mapeditor.h"
class mapEditor;

[xiphirx]

I think it should be

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#include "mapeditor.h"
class mapEditor;

Both ways are not working

[K-Bal]

You use the forward declaration in your header and the actual include in your source file.

[RyanPridgeon]

I think it should be

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#include "mapeditor.h"
class mapEditor;

Both ways are not working

No. Look, you should have a header with the class prototype, where you define the object as being part of your class. So for this, you don't need to know what the object does. You don't need to know its functions, members or usage. So you simply forward declare, such as

foo.h

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#ifndef SOMETHING
#define SOMETHING

class Bar;

class Foo {
    Bar* var;

    Foo();
};

#endif

Then when you want to use the object in your source file, you are free to INCLUDE the entire object's prototype, so that you can use the functions and members.

foo.cpp

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#include "foo.h"
#include "bar.h"

Foo::Foo(){
    var = new Bar();
    var->DoSomething();
    var->someMember = RANDOM_THING;
}

SO a recap. IN MOST CASES: In the header, you FORWARD DECLARE. In the source file, you INCLUDE.
edit:

That's about as good as I can explain it. I found this example code for you to look through if you're still having problems.
Example code for forward declaration
The trick is to think about what the compiler knows. If you say class Something; the compiler knows you have a class called Something, so you can hold pointers to it but you can't use it's functions because the compiler doesn't know about them.