Use RUNTIME_CLASS with the name of the class, as shown here for the class CObject:If you have derived your class from CObject and used the DECLARE_DYNAMIC and IMPLEMENT_DYNAMIC macros explained previously, the CObject class has the ability to determine the exact class of an object at run-time. This ability is an extension of the normal capabilities of C++.
The ability to determine the class of an object at run-time is most useful when extra type checking of function arguments is needed and when you must write special-purpose code based on the class of an object.
The CObject member function IsKindOf can be used to determine if a particular object belongs to a specified class or if it is derived from a specific class. The argument to IsKindOf is a CRuntimeClass, which you can get by using the RUNTIME_CLASS macro with the name of the class. The use of the RUNTIME_CLASS macro is shown below.
·To use the RUNTIME_CLASS macro:
Use RUNTIME_CLASS with the name of the class, as shown here for the class CObject:
CRuntimeClass* pClass = RUNTIME_CLASS( CObject );
You will rarely need to access the run-time class object directly. A more common use is to pass the run-time class object to the IsKindOf function, as shown in the next section.
·To use the IsKindOf function:
IsKindOf will test an object to see if it belongs to a particular class. The following steps show how to use IsKindOf.
1.Make sure the class has run-time class support. That is, the class must have been derived from CObject and used the DECLARE_DYNAMIC and IMPLEMENT_DYNAMIC macros explained previously on pages 264-265. (Since serialization support requires run-time class support, the class may have been defined with the DECLARE_SERIAL and IMPLEMENT_SERIAL macros.)
2.Call the IsKindOf member function for objects of that class, using the RUNTIME_CLASS macro to generate the CRuntimeClass argument, as shown here:
// in .H file
class CPerson : public CObject
{
DECLARE_DYNAMIC( CPerson )
public:
CPerson(){};
// other declaration stuff left out...
};
// in .CPP file
IMPLEMENT_DYNAMIC( CPerson, CObject )
CObject* myObject = new CPerson;
if( myObject->IsKindOf( RUNTIME_CLASS( CPerson ) ) )
{
//if IsKindOf is true, then cast is alright
CPerson* myPerson = (CPerson*) myObject;
}
Note:
IsKindOf returns TRUE if the object is a member of the specified class or of a class derived from the specified class. It only works properly in single-inheritance hierarchies.