FIX: copy() Member of _bstr_t in comutl.h Doesn't Copy

• The C/C++ Compiler (CL.EXE), included with:
  • Microsoft Visual C++, 32-bit Editions, version 5.0

SYMPTOMS

Calling the _bstr_t::copy member function does not return a copy of the contained BSTR and may cause an access violation in OLEAUT32.DLL when debugging. Sample code that demonstrates this bug is included below.

CAUSE

This is due to a bug in the implementation of a helper function of a nested class, _bstr_t::Data_t::Copy(). On line 627 of comutil.h the function is passing an uninitialized local variable to ::SysStringByteLen(bstr) instead of passing the member variable, m_wstr.

RESOLUTION

Replace the call to t1.copy() with SysAllocString(static_cast<const wchar_t*>(t1)) where t1 is an object of type _bstr_t.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been corrected in Visual Studio 97, Service Pack 1.

For additional information about the Visual Studio 97 Service Pack 1, please see the following article in the Microsoft Knowledge Base:

Q170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION

By stepping through the following sample code in the debugger, you can see that the string is not copied to t2.

Sample Code

   // Compile options needed: /Zi
   // Libraries needed: oleaut32.lib comsupp.lib
   #include <comutil.h>
   #include <windows.h>
   int main ()
   {
      _bstr_t t1 = "Hello";
      BSTR t2;
      t2 = t1.copy();
      t2 = SysAllocString(static_cast<const wchar_t*>(t1));  // workaround
      return 0;
   } 

Keywords : kbtool kbVS97sp1fix kbVS97sp2fix
Version : 5.0
Platform : NT WINDOWS
Issue type : kbbug