Article: Q192099
Product(s): Microsoft C Compiler
Version(s): winnt:4.0,5.0
Operating System(s):
Keyword(s): kberrmsg kbdocerr kbLangCPP kbMFC kbDocs kbVC400bug kbVC500bug kbVC600fix kbBug kbGrpDS
Last Modified: 27-JUL-2001
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The information in this article applies to:
- Microsoft Visual C++, version 4.0
- Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0
- Microsoft Visual C++, 32-bit Professional Edition, version 5.0
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SYMPTOMS
========
The following provides supplemental information to the documentation on
STATIC_DOWNCAST:
STATIC_DOWNCAST( class_name, pobject )
Parameters:
class_name
The name of the class you want to cast to.
pobject
The pointer to be cast to a pointer to a class_name object.
Remarks:
This macro casts pobject 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 and
if it points to an object that is not a "kind of" the class_name (see
definition for the CObject::IsKindOf). In non- _DEBUG builds, the macro
performs the cast without any type checking.
class_name must be derived from CObject and use the DECLARE_DYNAMIC and
IMPLEMENT_DYNAMIC, the DECLARE_DYNCREATE and IMPLEMENT_DYNCREATE, or the
DECLARE_SERIAL and IMPLEMENT_SERIAL macros explained in the Help topic
"CObject Class: Deriving a Class from Cobject."
For example, you might cast a pointer to CYourDocument, called pYourDoc, to a
pointer to CDocument using the following expression:
CDocument* pDoc = STATIC_DOWNCAST(CDocument, pYourDoc);
If pYourDoc does not point to an object derived directly or indirectly from
CDocument, the macro will ASSERT.
Similarly, the documentation on DYNAMIC_DOWNCAST should be supplemented by
saying that class_name must be derived from CObject and use the
DECLARE_DYNAMIC and IMPLEMENT_DYNAMIC, the DECLARE_DYNCREATE and
IMPLEMENT_DYNCREATE, or the DECLARE_SERIAL and IMPLEMENT_SERIAL macros.
If you leave out the pair of DECLARE_... and IMPLEMENT_... macros from your
code, trying to cast the class pointer using STATIC_DOWNCAST or
DYNAMIC_DOWNCAST gives compiler errors like the following:
error C2039: 'classCMyClass' : is not a member of 'CMyClass'
error C2065: 'classCMyClass' : undeclared identifier
STATUS
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MORE INFORMATION
================
Following is additional information on related subjects:
1. The documentation on CObject::IsKindOf should also include:
This function works only for classes declared with the
DECLARE_DYNAMIC, DECLARE_DYNCREATE, or DECLARE_SERIAL macros.
2. The documentation on DECLARE_DYNCREATE should also include:
The DECLARE_DYNCREATE macro includes all the functionality of
DECLARE_DYNAMIC.
3. You may also want to see the topics on the static_cast and dynamic_cast
operators in the Visual C++ documentation. Please note that the
STATIC_DOWNCAST and DYNAMIC_DOWNCAST macros suggest an action that is
contrary to the common usage of the term "downcast". The term "downcast" is
commonly used to signify the movement of an object down a class hierarchy,
from a given class to a class derived from it. This may be confusing when you
consider that the STATIC_DOWNCAST and DYNAMIC_DOWNCAST macros perform the
action of "upcasting". The term "upcast" is commonly used to signify the
movement of an object up the class hierarchy, from a derived class to a class
it is derived from.
REFERENCES
==========
Q151070 FIX: DYNAMIC_DOWNCAST & STATIC_DOWNCAST Causes Stack Overflow
Additional query words: DECLARE_DYNAMIC IMPLEMENT_DYNAMIC DECLARE_DYNCREATE IMPLEMENT_DYNCREATE DECLARE_SERIAL IMPLEMENT_SERIAL IsKindOf
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Keywords : kberrmsg kbdocerr kbLangCPP kbMFC kbDocs kbVC400bug kbVC500bug kbVC600fix kbBug kbGrpDSMFCATL kbISS
Technology : kbVCsearch kbVC400 kbAudDeveloper kbVC500 kbVC32bitSearch kbVC500Search
Version : winnt:4.0,5.0
Issue type : kbbug
Solution Type : kbfix
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