What is CRuntime class? Where it is used?

CRuntimeClass Structure

CRuntimeClass is a structure to hold the runtime type, name, parent class and methods to indentify class information and dynamic creation function. MFC base class CObject holds CRuntimeClass and thus each class derived from CObject is associated with a CRuntimeClass structure that you can use to obtain information about an object or its base class at run time. Here are CRuntimeClass methods and member variables.

CRuntimeClass Methods

Name	Description
CreateObject	Creates an object during run time.
FromName	Creates an object during run time using the familiar class name.
IsDerivedFrom	Determines if the class is derived from the specified class.

CRuntimeClass Members

m_lpszClassName	The name of the class.
m_nObjectSize	The size of the object in bytes.
m_pBaseClass	A pointer to the CRuntimeClass structure of the base class.
m_pfnCreateObject	A pointer to the function that dynamically creates the object.
m_pfnGetBaseClass	Returns the CRuntimeClass structure (only available when dynamically linked).
m_wSchem	The schema number of the class.

CreateObject/m_pfnCreateObject

class CMyClass : public CWnd
{
  DECLARE_DYNCREATE(CMyClass);
};
IMPLEMENT_DYNCREATE(CMyClass,CWnd)

int main() 
{
  CRuntimeClass* pClass = RUNTIME_CLASS(CMyClass);
  CObject* pObject = pClass->m_pfnCreateObject();
  or
  CObject* pObject = pClass->CreateObject();
}

CRuntimeClass::FromName

CRuntimeClass* pClass = CRuntimeClass::FromName(_T("CMyClass"));
if (pClass == NULL)
{
 // not found, display a warning for diagnostic purposes
 AfxMessageBox(_T("Warning: CMyClass not defined"));
 return NULL;
}

CRuntimeClass::IsDerivedFrom

// We only want to create an object derived from CWnd.
if (!pClass->IsDerivedFrom(RUNTIME_CLASS(CWnd)))
{
 TRACE(_T("Error; Object %s is not derived from CWnd\n"),
	pClass->m_lpszClassName);
 return FALSE;
}

ClassName, BaseClass, size, schema

// Get a pointer to the base class CRuntimeClass.
#ifdef _AFXDLL
 CRuntimeClass* pBaseClass = pClass->m_pfnGetBaseClass();
#else
 CRuntimeClass* pBaseClass = pClass->m_pBaseClass;
#endif
ASSERT(pBaseClass != NULL);

TRACE("Creating object %s derived from %s, with object size %d "
 "and schema %d\n", pClass->m_lpszClassName, 
 pBaseClass->m_lpszClassName, pClass->m_nObjectSize, 
 pClass->m_wSchema);

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