BUG: Vector Delete Calls Exported Destructor Only Once (121216)
The information in this article applies to:
- Microsoft Visual C++ for Windows, 16-bit edition 1.0
- Microsoft Visual C++ for Windows, 16-bit edition 1.5
- Microsoft Visual C++, 32-bit Editions 1.0
- Microsoft Visual C++, 32-bit Editions 2.0
- Microsoft Visual C++, 32-bit Editions 4.0
- Microsoft Visual C++, 32-bit Editions 4.1
- Microsoft Visual C++, 32-bit Editions 4.2
- Microsoft Visual C++, 32-bit Editions 5.0
- Microsoft Visual C++, 32-bit Editions 6.0
- Microsoft Visual C++ .NET (2002)
This article was previously published under Q121216 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.
| Modification Type: | Minor | Last Reviewed: | 7/5/2005 |
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| Keywords: | kbBug kbCompiler kbfix KB121216 |
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