DOCUMENT:Q121216 17-FEB-2002 [visualc] TITLE :BUG: Vector Delete Calls Exported Destructor Only Once PRODUCT :Microsoft C Compiler PROD/VER::1.0,1.5,2.0,4.0,4.1,4.2,5.0,6.0 OPER/SYS: KEYWORDS:kbCompiler kbVC100bug kbVC150bug kbVC200bug kbVC400bug kbVC410bug kbVC420bug kbVC500bug ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft C/C++ Compiler (CL.EXE), used with: - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5 - Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 4.0, 4.1, 4.2, 5.0, 6.0 - Microsoft Visual C++.NET (2002) ------------------------------------------------------------------------------- SYMPTOMS ======== A call to the vector delete operator on a class defined in a DLL calls the destructor for the object only once. This problem occurs only if the destructor is virtual and the DLL itself does not reference the vector memory allocation functions (new [] or delete []). CAUSE ===== The code generated by the compiler to perform vector deleting of objects is done by generating a call to an internal function. This internal function is generated by the compiler. The problem is due to an incorrect compiler optimization. The compiler assumes that if a module (EXE or DLL) never makes reference to the vector memory operators, then the internal function that handles the vector deleting is not needed. This is a valid optimization for an EXE but not for a DLL. Therefore, this statement: delete [] pClass Ends up being basically the same as: delete pClass RESOLUTION ========== To work around this problem, you must force your DLL to reference the vector deleting destructor. The memory allocation functions don't actually need to be called. The compiler just needs to see them. This can be done by generating a dummy function that is never called but that is linked in to the DLL. For example: void ForceVectors() { CMyClass *pClass = new CMyClass[2]; CMyClass *pOtherClass = new CMyOtherClass[2]; }; static (void *pFunc)() = ForceVectors; The reference to the static variable initialization (pFunc) forces the function ForceVectors to be linked in. This then forces the DLL to have the vector deleting destructors for the classes (CMyClass and CMyOtherClass). Place this code in any module in your DLL. STATUS ====== Microsoft has confirmed this to be a bug in the products listed at the beginning of this article. This bug was corrected in Visual C++ version 5.0 to generate correct behavior in the case where the entire class is exported. The bug (and workaround) remains for the case where the class is not exported, but individual class members are exported. Additional query words: ====================================================================== Keywords : kbCompiler kbVC100bug kbVC150bug kbVC200bug kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600bug Technology : kbVCsearch kbAudDeveloper kbCVCComp Version : :1.0,1.5,2.0,4.0,4.1,4.2,5.0,6.0 Issue type : kbbug Solution Type : kbfix ============================================================================= 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 2002.