DOCUMENT:Q192561 26-JUN-2001 [visualc] TITLE :PRB: Error C2787 When Building a Project Using ATL 3.0 PRODUCT :Microsoft C Compiler PROD/VER:WINDOWS:3.0 OPER/SYS: KEYWORDS:kbCOMt kbVC600 kbATL300 kbGrpDSMFCATL kbMIDL ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - The Microsoft Active Template Library (ATL) 3.0, used with: - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 ------------------------------------------------------------------------------- SYMPTOMS ======== When building a project with ATL 3.0 you may get a compiler error c2787 (no GUID has been associated with this object). CAUSE ===== The newer versions of MIDL use the compiler facility [__declspec(uuid())] to tag a GUID to an interface in the header files it generates. ATL version 3.0 makes use of this fact in the implementation of COM_INTERFACE_ENRY macro; it now uses the keyword __uuidof() to extract the interface ID from the MIDL-generated header. ATL 2.1 uses the token pasting operator (IID_##IFoo) to get the interface ID. This action requires including the MIDL-generated header and also the "project_i.c", which MIDL generated. If you use an older MIDL-generated header file [which does not use __declspec(uuid())] with ATL 3.0, you will get this compiler error, because __uudiof() can't extract the interface ID. RESOLUTION ========== Define the preprocessor symbol _ATL_NO_UUIDOF in the C/C++ tab of the Project Settings dialog box. This forces ATL to use the token pasting operator (##) rather than __uuidof() when forming the interface ID. STATUS ====== This behavior is by design. MORE INFORMATION ================ Sample Code ----------- COM_INTERFACE_ENTRY in ATL 2.1 #define COM_INTERFACE_ENTRY(x)\ {&IID_##x), \ offsetofclass(x, _ComMapClass), \ _ATL_SIMPLEMAPENTRY}, COM_INTERFACE_ENTRY in ATL 3.0 #ifndef _ATL_NO_UUIDOF #define _ATL_IIDOF(x) __uuidof(x) #else #define _ATL_IIDOF(x) IID_##x #endif #define COM_INTERFACE_ENTRY(x)\ {&_ATL_IIDOF(x), \ offsetofclass(x, _ComMapClass), \ _ATL_SIMPLEMAPENTRY}, Newer MIDL headers files use the macros DECLSPEC_UUID() or MIDL_INTERFACE(), which expand to __declspec(uuid()). MIDL versions 3.01.75 and later use the __declspec directive. REFERENCES ========== "Porting from ATL 2.1" in the online help. (c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Jaganathan Thangavelu, Microsoft Corporation. (c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Jaganathan Thangavelu, Microsoft Corporation Additional query words: kbDSupport ====================================================================== Keywords : kbCOMt kbVC600 kbATL300 kbGrpDSMFCATL kbMIDL Technology : kbAudDeveloper kbATLsearch Version : WINDOWS:3.0 Issue type : kbprb ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.