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Learn more about: Type Casting of MFC Class Objects |
Type Casting of MFC Class Objects |
11/04/2016 |
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Type casting macros provide a way to cast a given pointer to a pointer that points to an object of specific class, with or without checking that the cast is legal.
The following table lists the MFC type casting macros.
| Name | Description |
|---|---|
| DYNAMIC_DOWNCAST | Casts a pointer to a pointer to a class object while checking to see if the cast is legal. |
| STATIC_DOWNCAST | Casts a pointer to an object from one class to a pointer of a related type. In a debug build, causes an ASSERT if the object is not a "kind of" the target type. |
Provides a handy way to cast a pointer to a pointer to a class object while checking to see if the cast is legal.
DYNAMIC_DOWNCAST(class, pointer)
class
The name of a class.
pointer
A pointer to be cast to a pointer to an object of type class.
The macro will cast the pointer parameter to a pointer to an object of the class parameter's type.
If the object referenced by the pointer is a "kind of" the identified class, the macro returns the appropriate pointer. If it is not a legal cast, the macro returns NULL.
Casts pobject to a pointer to a class_name object.
STATIC_DOWNCAST(class_name, pobject)
class_name
The name of the class being cast to.
pobject
The pointer to be cast to a pointer to a class_name object.
pobject must either be NULL, or point to an object of a class which is derived directly, or indirectly, from class_name. In builds of your application with the _DEBUG preprocessor symbol defined, the macro will ASSERT if pobject is not NULL, or if it points to an object that is not a "kind of" the class specified in the class_name parameter (see CObject::IsKindOf). In non- _DEBUG builds, the macro performs the cast without any type checking.
The class specified in the class_name parameter must be derived from CObject and must use the DECLARE_DYNAMIC and IMPLEMENT_DYNAMIC, the DECLARE_DYNCREATE and IMPLEMENT_DYNCREATE, or the DECLARE_SERIAL and IMPLEMENT_SERIAL macros as explained in the article CObject Class: Deriving a Class from CObject.
For example, you might cast a pointer to CMyDoc, called pMyDoc, to a pointer to CDocument using this expression:
[!code-cppNVC_MFCDocView#197]
If pMyDoc does not point to an object derived directly or indirectly from CDocument, the macro will ASSERT.