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Emulation of CRuntimeClass for non-CObject derived classes

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20 Feb 2010CPOL 22.8K   80   4   7
MACROs having advantage of CRuntimeClass for non-CObject derived classes.

Introduction

Let's assume you decided to create a hierarchy of non-CObject derived classes using the CRuntimeClass of MFC libraries (and DECLARE_DYNAMIC IMPLEMENT_DYNAMIC DECLARE_DYNCREATE IMPLEMENT_DYNCREATE as well). It is implied that your base class is named like CXxx (C + class prefix) and all your child classes have names according to the rule: C+ class prefix + kind_name (for example, CXxxCool, CXxxAdvanced, CXxxSuper etc.). You need to have a static function Create(string kind_name) to create objects at runtime and a function GetKind returning a string with a 'kind_name' of the object.

Background

Unlike CRuntimeClass (actually it is a structure), our 'CKindOf...' class exists as MACROs DECLARE_KIND_OF(class_name) and IMPLIMENT_KIND_OF(class_name), and every generated 'KindOf' class corresponds with a given class hierarchy.

C++
DECLARE_KIND_OF(Xyz)

IMPLIMENT_KIND_OF(Xyz)

Using the code

The base class of your hierarchy should use the DECLARE_BASE_DYNCLASS(class_name) and IMPLIMENT_BASE_DYNCLASS(class_name) MACROs.

C++
class CXyz
{

public:
    CXyz();
DECLARE_BASE_DYNCLASS(Xyz)
};

IMPLIMENT_BASE_DYNCLASS(Xyz)
CXyz::CXyz()
{

}

And every child class should use DECLARE_CHILD_DYNCLASS(class_name,kind_name) and IMPLIMENT_CHILD_DYNCLASS(class_name,kind_name,parent_name).

C++
class CXyzCool:public CXyz
{
  DECLARE_CHILD_DYNCLASS(Xyz,Cool)
};

IMPLIMENT_CHILD_DYNCLASS(Xyz,Cool,Base)

class CXyzAdv:public CXyzCool
{
  DECLARE_CHILD_DYNCLASS(Xyz,Adv)
};

IMPLIMENT_CHILD_DYNCLASS(Xyz,Adv,Cool)

If your child class is derived directly from the base class (the second level in the class hierarchy), use the 'Base' keyword as the third argument.

IMPLIMENT_CHILD_DYNCLASS(Xyz,Cool,Base)

And the prefix of the base class otherwise:

C++
IMPLIMENT_CHILD_DYNCLASS(Xyz,Adv,Cool)

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Software Developer (Senior) Elstab
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Comments and Discussions

 
GeneralDerived class name for non-CObject derived classes Pin
geoyar23-Feb-10 7:29
professionalgeoyar23-Feb-10 7:29 
GeneralRe: Derived class name for non-CObject derived classes Pin
cyberanarchist23-Feb-10 19:26
cyberanarchist23-Feb-10 19:26 
GeneralRe: Derived class name for non-CObject derived classes Pin
geoyar25-Feb-10 4:31
professionalgeoyar25-Feb-10 4:31 
There is the standard C++ operator 'typeid' to do all runtime work.
From MS VS 2008 help file:

"The typeid operator allows the type of an object to be determined at run time.

The result of typeid is a const type_info&. The value is a reference to a type_info object that represents either the type-id or the type of the expression, depending on which form of typeid is used. See type_info Class for more information.

The typeid operator does not work with managed types (abstract declarators or instances), see typeid for information on getting the Type of a specified type.

The typeid operator does a run-time check when applied to an l-value of a polymorphic class type, where the true type of the object cannot be determined by the static information provided. Such cases are:

A reference to a class

A pointer, dereferenced with *

A subscripted pointer (i.e. [ ]). (Note that it is generally not safe to use a subscript with a pointer to a polymorphic type.)

If the expression points to a base class type, yet the object is actually of a type derived from that base class, a type_info reference for the derived class is the result. The expression must point to a polymorphic type (a class with virtual functions). Otherwise, the result is the type_info for the static class referred to in the expression. Further, the pointer must be dereferenced so that the object it points to is used. Without dereferencing the pointer, the result will be the type_info for the pointer, not what it points to. For example:

Copy Code
// expre_typeid_Operator.cpp
// compile with: /GR /EHsc
#include <iostream>
#include <typeinfo.h>

class Base {
public:
virtual void vvfunc() {}
};

class Derived : public Base {};

using namespace std;
int main() {
Derived* pd = new Derived;
Base* pb = pd;
cout << typeid( pb ).name() << endl; //prints "class Base *"
cout << typeid( *pb ).name() << endl; //prints "class Derived"
cout << typeid( pd ).name() << endl; //prints "class Derived *"
cout << typeid( *pd ).name() << endl; //prints "class Derived"
delete pd;
}"

Are your macros do it better?
geoyar

GeneralRe: Derived class name for non-CObject derived classes Pin
cyberanarchist26-Feb-10 2:02
cyberanarchist26-Feb-10 2:02 
GeneralSome Explaination Pin
JohnWallis4221-Feb-10 10:11
JohnWallis4221-Feb-10 10:11 
GeneralRe: Some Explaination [modified] Pin
cyberanarchist21-Feb-10 16:41
cyberanarchist21-Feb-10 16:41 
GeneralRe: Some Explaination Pin
JohnWallis4221-Feb-10 17:11
JohnWallis4221-Feb-10 17:11 

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