Programming with Microsoft Visual C++.NET 6ed [Electronic resources] نسخه متنی

A Sample Program

Here's the code for a command-line program that dynamically constructs objects of two classes. This isn't real MFC code—the CObject class is a simplified version of the MFC library CObject class. You can find this code in the

dyncreat.cpp file in the \vcppnet\appendb folder on the companion CD.

// dyncreat.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <stdio.h>
#define RUNTIME_CLASS(class_name) (&class_name::class##class_name)
class CObject;
struct CRuntimeClass
{
char m_lpszClassName[21];
int m_nObjectSize;
CObject* (*m_pfnCreateObject)();
CObject* CreateObject();
};
// Not a true abstract class because there are no pure 
//  virtual functions, but user can't create CObject objects 
//  because of the protected constructor
class CObject
{
public:
// not pure because derived classes don't necessarily
// implement it
virtual CRuntimeClass* GetRuntimeClass() const { return NULL; }
// We never construct objects of class CObject, but in MFC we
//  use this to get class hierarchy information.
static CRuntimeClass classCObject;        // DYNAMIC
virtual ~CObject() {};  // gotta have it
protected:
CObject() { printf("CObject constructor\n"); }
};
CRuntimeClass CObject::classCObject = { "CObject", 
sizeof(CObject), NULL };
CObject* CRuntimeClass::CreateObject()
{
return (*m_pfnCreateObject)(); // indirect function call
}
class CAlpha : public CObject
{
public:
virtual CRuntimeClass* GetRuntimeClass() 
const { return &classCAlpha; }
static CRuntimeClass classCAlpha;        // DYNAMIC
static CObject* CreateObject();          // DYNCREATE
protected:
CAlpha() { printf("CAlpha constructor\n"); }
};
CRuntimeClass CAlpha::classCAlpha = { "CAlpha", 
sizeof(CAlpha), CAlpha::CreateObject };
CObject* CAlpha::CreateObject() // static function
{
return new CAlpha;    
}
class CBeta : public CObject
{
public:
virtual CRuntimeClass* GetRuntimeClass() 
const { return &classCBeta; }
static CRuntimeClass classCBeta;         // DYNAMIC
static CObject* CreateObject();          // DYNCREATE
protected:
CBeta() { printf("CBeta constructor\n"); }
};
CRuntimeClass CBeta::classCBeta = { "CBeta", 
sizeof(CBeta), CBeta::CreateObject };
CObject* CBeta::CreateObject() // static function
{
return new CBeta;    
}
int main()
{
printf("Entering dyncreate main\n");
CRuntimeClass* pRTCAlpha = RUNTIME_CLASS(CAlpha);
CObject* pObj1 = pRTCAlpha->CreateObject();
printf("class of pObj1 = %s\n", 
pObj1->GetRuntimeClass()->m_lpszClassName);
CRuntimeClass* pRTCBeta = RUNTIME_CLASS(CBeta);
CObject* pObj2 = pRTCBeta->CreateObject();
printf("class of pObj2 = %s\n", 
pObj2->GetRuntimeClass()->m_lpszClassName);
delete pObj1;
delete pObj2;
return 0;
}