I have the following code, there is an 'Face' class which is composed of an 'Eyebrow' class. The expression of the face can be changed to one of the allowed public enums, thus controlling how each of it's constituent should be changed. Each of the constituent classes should be responsible for responding to a changed expression which is why I want to pass that along to each constituent.
face.h:
#include "eyebrow.h"
class Face {
public:
enum Expression {NEUTRAL, JOY, ANGER};
void setExpression(Expression);
private:
Eyebrow left_eyebrow;
}
face.cpp:
#include "face.h"
#include "eyebrow.h"
void Face::setExpression(Expression e) {
left_eyebrow.setExpression(e);
}
eyebrow.h:
#include "face.h"
class Eyebrow {
public:
void setExpression(Face::Expression);
};
The code is being compiled with Cmake:
add_executable(Main main.cpp face.cpp eyebrow.cpp)
I am getting the following compiler error: ‘Face’ has not been declared in void setExpression(Face::Expression_e) in eyebrow.h.
I then forward declared Face (see below) and got the compiler error: ‘Face::Expression’ has not been declared in void setExpression(Face::Expression); in eyebrow.h
eyebrow.h (with forward declaration):
#include "face.h"
class Face;
class Eyebrow {
public:
void setExpression(Face::Expression);
};
What is the recommended way of solving this, should friends be used?
You have created a circular dependency:
face.h includes eyebrow.h and eyebrow.h includes face.h, so they're including each other. You must resolve the circular dependency.
You could remove the enum from Face and put it in its own header file, which both files could then include.
Alternatively, you could store a pointer to Eyebrow in Face instead of Eyebrow itself. Then you could remove the include of eyebrow.h in face.h and forward-declare Eyebrow instead. The pointer can then be initialized in the constructor of Face.
Related
This question already has answers here:
Resolve build errors due to circular dependency amongst classes
(12 answers)
Closed 2 years ago.
So, I know that there are many questions on stack overflow out there that are trying to handle circular dependencies. But none of those could really answer my question, if it is possible to have two classes know each other, and, more importantly, access information from each other. So, basically, I have read that you could use forward decleration, but with forward decleration, I couldn't access any fields. Maybe I should also add that I am really new to C++.But enough talking, let's get to an example:
Let's say we have a class called Scene and a class called EntityBase, which are defined as following:
EntityBase.h
#pragma once
#include <string>
#include "Scene.h"
class EntityBase
{
public:
std::string entityId;
Scene scene;
EntityBase(std::string entityId);
/*
This method will be called when this object is added to the scene
*/
void onAddedToScene(Scene* scene);
/*
This method will be called when this object is removed from the scene
*/
void onRemovedFromScene(Scene* scene);
};
Scene.h
#pragma once
#include <vector>
#include <string>
#include "EntityBase.h"
class Scene
{
public:
std::vector<EntityBase> entities;
std::string name;
Scene(std::string name);
void addToScene(EntityBase& entityBase);
};
The question arises,
How can I print out the name of Scene(and use every method of Scene) while EntityBase can fully access Scene too?
So, I'd really appreciate if you'd tell how to do this, because I will probably need to access every field and/or method later.
Since the C++17 standard you don't need the full EntityBase class definition for the Scene class, only a forward declaration:
#pragma once
#include <vector>
#include <string>
class EntityBase; // Forward declaration
class Scene
{
public:
std::vector<EntityBase> entities;
std::string name;
Scene(std::string name);
void addToScene(EntityBase& entityBase);
};
You of course need to include EntityBase.h anywhere where the entities vector is used, most notable in the Scene.cpp source file.
Since EntityBase is using an actual instance of Scene you can't do the same with that class and the EntityBase.h header file. Here you must include the Scene.h header file.
If you build targeting an older C++ standard (C++14 or earlier) then you must have the full definition of the EntityBase class for the vector.
As a possible workaround either make entities a vector of pointers to EntityBase; Or make EntityBase::scene a pointer and use forward declaration in the EntityBase.h header file instead. Or a combination of both.
Currently I have 3 classes, set up like this:
World.h
include "WorldObject.h"
class WorldObject;
class TextObject; // when this is added, compiles fine, but tobj is incomplete when accessed
//(world->tobj->function()). if #include "TextObject.h" is added, numerous errors occur within TextObject.h
class World {
public:
WorldObject* wobj; // works fine
TextObject* tobj; //trying to get this to be functional
};
WorldObject.h
#include "World.h"
class World;
class WorldObject {
public:
WorldObject(World* world){...} // works fine, world can be accessed from world objects
};
TextObject.h
#include "WorldObject.h"
#include "World.h"
class TextObject : WorldObject {
public:
TextObject(World* world) : WorldObject(w){...};
};
How can I use forward declaration so that tobj will be accessible from World.h, as obj is, with no errors? I am also using #pragma once at the beginning of each class. I have attempted to add "class World" to TextObject.h and "class TextObject" to World.h, but none of the seemingly standard procedures are working. Any suggestions?
#include <WorldObject.h> in your .cpp file rather than your header and you can access it from there.
Your header includes are causing circular dependencies, which you avoid through forward declarations.
I have three classes.
first class:
#ifndef C_LINKED_LIST_H
#define C_LINKED_LIST_H
class CLinkedList {
private:
//removed code for brevity
public:
// removed code for brevity
};
#endif
second class:
#ifndef C_SSF_FOLDER_CONTAINER_H
#define C_SSF_FOLDER_CONTAINER_H
#include "C_SSF_Folder.h"
#include "CLinkedList.h"
class C_SSF_Folder_Container {
private:
// removed code for brevity
public:
int Add_Folder(C_SSF_Folder *_pcl_SSF_Folder);
C_SSF_Folder *Get_Folder(int _i_Index);
C_SSF_Folder *Get_Folder(char *_pch_Name);
//^-----errors
};
#endif C_SSF_FOLDER_CONTAINER_H
my third class
#ifndef C_SSF_FOLDER_H
#define C_SSF_FOLDER_H
#include <windows.h>
#include <fstream>
#include "C_SSF_Folder_Container.h"
using namespace std;
class C_SSF_Folder {
public:
private:
C_SSF_Folder_Container cl_SSFFC_Folder_Container;
public:
};
#endif
my third class C_SSF_Folder.
I am including "C_SSF_Folder_Container.h"
and declaring a C_SSF_Folder_Container container.
Before declaring the variable it compiles fine. After I declare it
I get syntax errors in my C_SSF_Folder_Container
Severity Code Description Project File Line Suppression State
Error C2061 syntax error: identifier 'C_SSF_Folder' CSSFileSystem\projects\cssfilesystem\cssfilesystem\c_ssf_folder_container.h 16
Error C2061 syntax error: identifier 'C_SSF_Folder' CSSFileSystem \projects\cssfilesystem\cssfilesystem\c_ssf_folder_container.h 19
As I myself look into it I think there is a problem because my C_SSF_Folder is including C_SSF_Folder_Container.
and C_SSF_Folder_Container is including C_SSF_Folder
but the defines should take care of it? Other than that I have no clue what's the problem.
Everything is typed correctly.
You've got a circular #include -- C_SSF_Folder_Container.h #includes C_SSF_Folder.h and C_SSF_Folder.h #includes C_SSF_Folder_Container.h.
This would cause an infinite regress (and a compiler crash) except that you've got the #ifndef/#define guards at the top of your files (as you should); and because of them, instead what you get is that one of those two .h files can't see the other one, and that's why you get those errors.
The only way to fix the problem is to break the circle by deleting one of the two #includes that comprise it. I suggest deleting the #include "C_SSF_Folder.h" from C_SSF_Folder_Container.h and using a forward declaration (e.g. class C_SSF_Folder; instead.
C_SSF_Folder.h and C_SSD_Folder_Container.h are including each other(Circular Dependency).
When the compiler compiles C_SSF_Folder_Container object, it needs to create a C_SSF_Folder object as its field, however, the compiler needs to know the size of C_SSF_Folder object, so it reaches C_SSF_Folder object and tries to construct it. Here is the problem, when the compiler is constructing C_SSF_Folder object, the object has a C_SSF_Folder_Container object as its field, which is a typical chicken and egg question, both files depends on each other in order to compile.
So the correct way to do it is to use a forward declaration to break the circular dependency(including each other).
In your C_SSF_Folder.h, make a forward declaration of C_SSF_Folder_Container.
#include <windows.h>
#include <fstream>
using namespace std;
class C_SSF_Folder_Container;
class C_SSF_Folder {
public:
private:
C_SSF_Folder_Container cl_SSFFC_Folder_Container;
public:
};
#endif
Finally, include C_SSF_Folder_Container.h in your C_SSF_Folder.cpp.
You can also learn more in the following links:
Circular Dependency (Wiki):
https://en.wikipedia.org/wiki/Circular_dependency
Forward Declaration by Scott Langham
What are forward declarations in C++?
I can't solve this circular dependency problem; always getting this error:
"invalid use of incomplete type struct GemsGame"
I don't know why the compiler doesn't know the declaration of GemsGame even if I included gemsgame.h
Both classes depend on each other (GemsGame store a vector of GemElements, and GemElements need to access this same vector)
Here is partial code of GEMELEMENT.H:
#ifndef GEMELEMENT_H_INCLUDED
#define GEMELEMENT_H_INCLUDED
#include "GemsGame.h"
class GemsGame;
class GemElement {
private:
GemsGame* _gemsGame;
public:
GemElement{
_gemsGame = application.getCurrentGame();
_gemsGame->getGemsVector();
}
};
#endif // GEMELEMENT_H_INCLUDED
...and of GEMSGAME.H:
#ifndef GEMSGAME_H_INCLUDED
#define GEMSGAME_H_INCLUDED
#include "GemElement.h"
class GemsGame {
private:
vector< vector<GemElement*> > _gemsVector;
public:
GemsGame() {
...
}
vector< vector<GemElement*> > getGemsVector() {
return _gemsVector;
}
}
#endif // GEMSGAME_H_INCLUDED
Remove the #include directives, you already have the classes forward declared.
If your class A needs, in its definition, to know something about the particulars of class B, then you need to include class B's header. If class A only needs to know that class B exists, such as when class A only holds a pointer to class B instances, then it's enough to forward-declare, and in that case an #include is not needed.
If you deference the pointer and the function is inline you will need the full type. If you create a cpp file for the implementation you can avoid the circular dependecy (since neither of the class will need to include each others .h in their headers)
Something like this:
your header:
#ifndef GEMELEMENT_H_INCLUDED
#define GEMELEMENT_H_INCLUDED
class GemsGame;
class GemElement {
private:
GemsGame* _gemsGame;
public:
GemElement();
};
#endif // GEMELEMENT_H_INCLUDED
your cpp:
#include "GenGame.h"
GenElement::GenElement()
{
_gemsGame = application.getCurrentGame();
_gemsGame->getGemsVector();
}
Two ways out:
Keep the dependent classes in the same H-file
Turn dependency into abstract interfaces: GemElement implementing IGemElement and expecting for IGemsGame, and GemsGame implementing IGemsGame and containing a vector of IGemElement pointers.
Look at the top answer of this topic: When can I use a forward declaration?
He really explains everything you need to know about forward declarations and what you can and cannot do with classes that you forward declare.
It looks like you are using a forward declaration of a class and then trying to declare it as a member of a different class. This fails because using a forward declaration makes it an incomplete type.
I checked out a post similar to this but the linkage was different the issue was never resolved. The problem with mine is that for some reason the linker is expecting there to be a definition for the base class, but the base class is just a interface. Below is the error in it's entirety
c:\users\numerical25\desktop\intro todirectx\godfiles\gxrendermanager\gxrendermanager\gxrendermanager\gxdx.h(2) : error C2504: 'GXRenderer' : base class undefined
Below is the code that shows how the headers link with one another
GXRenderManager.h
#ifndef GXRM
#define GXRM
#include <windows.h>
#include "GXRenderer.h"
#include "GXDX.h"
#include "GXGL.h"
enum GXDEVICE {
DIRECTX,
OPENGL
};
class GXRenderManager {
public:
static int Ignite(GXDEVICE);
private:
static GXRenderer *renderDevice;
};
#endif
at the top of GxRenderManager, there is GXRenderer , windows, GXDX, GXGL headers. I am assuming by including them all in this document. they all link to one another as if they were all in the same document. correct me if I am wrong cause that's how a view headers. Moving on...
GXRenderer.h
class GXRenderer {
public:
virtual void Render() = 0;
virtual void StartUp() = 0;
};
GXGL.h
class GXGL: public GXRenderer {
public:
void Render();
void StartUp();
};
GXDX.h
class GXDX: public GXRenderer {
public:
void Render();
void StartUp();
};
GXGL.cpp and GXDX.cpp respectively
#include "GXGL.h"
void GXGL::Render()
{
}
void GXGL::StartUp()
{
}
//...Next document
#include "GXDX.h"
void GXDX::Render()
{
}
void GXDX::StartUp()
{
}
Not sure whats going on. I think its how I am linking the documents, I am not sure.
The problem is You need to have #include "GXRenderer.h" at the top of both: GXGL.h and also GXDX.h.
The base type must be defined not just declared before defining a derived type.
By the way, the error is a compiling error not linking error.
Edit: About your class type redefinition:
at the top of every header file you should have #pragma once.
The #pragma once directive specifies that the file will be included at most once by the compiler in a build.
You included them all into GXRenderManager.h, meaning that GXRenderManager.h is OK.
But you forgot to include them all into GXGL.cpp and GXDX.cpp. In these .cpp files GXRenderer class is completely unknown.
There are at least two "schools" of #include strategies. One says that header file must include everything that is needed for its own compilation. That would mean that GXGL.h and GXDX.h must include GXRenderer.h. If you followed that strategy, your GXGL.cpp and GXDX.cpp would be OK as they are now.
Another "school" says that header files must not include each other at all, i.e. all inclusions must be done through .cpp files. At first sight one could guess that your GXGL.h and GXDX.h follow that strategy (since you are not including anything into them), but then your GXRenderManager.h looks completely different.
You need to decide which strategy you are trying to follow and follow it. I'd recommend the first one.
I got an error C2504: 'CView' : base class undefined
where CView is not directly my base class from which I am inheriting.
I am inherting mYClass from MScrollView, "for this matter any class which is not actual Base Class is what the point is to be noted down here"
but the error is the C2504. When I have included it in the header where this problem is arising, this problem is resolved.
#include "stdafx.h"
where stdafx.h has #include which contains all the basic class defined...hope this answer resolves everyone who are facing this issue.