Application Verifier leak

Question

I have a C++ Windows Mobile 5 (ARMV4I) Visual Studio 2008 project. I'm using Application Verifier to check for memory leaks.

In one DLL loaded by the project, Application verifier sees a memory leak:

TrackedItem count: 1
Callstack:
   0x2d87406c: shim_verifier.dll!(null) + 406ch
Unable to open '\windows\ole32.map' (GLE: 2)
   0x03116410: ole32.dll!(null) + 2410h
   0x030fa810: oleaut32.dll!(null) + 15810h
   0x030ec024: oleaut32.dll!(null) + 7024h
   0x030ef3cc: oleaut32.dll!(null) + a3cch
   0x030ef5c8: oleaut32.dll!(null) + a5c8h
   0x78264858: MyLibrary.dll!(null) + 4858h
   0x782646fc: MyLibrary.dll!(null) + 46fch
   0x78261bac: MyLibrary.dll!(null) + 1bach
   0x2c0112c8: !(null) + 112c8h
   0x2c011988: !(null) + 11988h
   0x03f67270: coredll.dll!(null) + 1d270h
Leaked items:
   0x878e69cc   (oleaut32.dll)

This address corresponds to a line in the DLL that instances a CComBSTR():

HRESULT SomeFunction( LPCTSTR some_string )
{
    HRESULT hr = GetTheErrorCode();
    CComBSTR bstr( some_string ); // leak here
    /*
        The lines that would have used the bstr are commented
        out. It is never actually used in the function anymore.
    */

    return hr;
}

The easy solution is to remove the line that creates the CComBSTR. Unfortunately, it's not my code to change. I just want to know why Application Verifier is flagging this as a leak. I thought CComBSTR automatically called ::SysFreeString() in its destructor.

Thanks,
PaulH

Answer 1

It is possible to explicitly free it. Try freeing and run AppVerifier.
Hope this helps.

// Declare a CComBSTR object
CComBSTR bstrMyString( "Hello World" );
// Free the string explicitly
::SysFreeString(bstrMyString);
// The string will be freed a second time
// when the CComBSTR object goes out of scope,
// which is invalid.

Taken from
http://msdn.microsoft.com/en-us/library/bdyd6xz6%28VS.80%29.aspx#programmingwithccombstr_explicitlyfreeing

Answer 2

This is probably a false positive caused by COM's caching BSTR's see Raymond's post here

http://blogs.msdn.com/b/oldnewthing/archive/2009/11/27/9929238.aspx

You should set the OANOCACHE environment variable when checking for leaks.