Will SysAllocString allocation be GC'ed

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

Peggy - 29 Aug 2006 10:10 GMT

Hi

I have an unmanaged dll which returns a BSTR* allocated using a
SysAllocString on the unmanaged code.

Now when this BSTR is returned to the Managed world, will the memory
allocated to the BSTR be freed by GC or do I need to take care of
clearing off the Allocated memory?

Regards
Pawan Arya

Reply to this Message

Willy Denoyette [MVP] - 29 Aug 2006 20:05 GMT

| Hi
|
[quoted text clipped - 7 lines]
| Regards
| Pawan Arya

Unmanaged resources aren't freed by the GC, it's your responsability to free
the BSTR*.

Willy.

Reply to this Message

Mattias Sjögren - 29 Aug 2006 21:15 GMT

>Now when this BSTR is returned to the Managed world, will the memory
>allocated to the BSTR be freed by GC or do I need to take care of
>clearing off the Allocated memory?

The CLR will free the BSTR during the marshaling process if the
function has been declared correctly.

Mattias

Signature

Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

Reply to this Message

Peggy - 30 Aug 2006 00:17 GMT

> The CLR will free the BSTR during the marshaling process if the
> function has been declared correctly.

Hi Mattias

Here's the declaration and how it is used in the C# code.

//*******DECLARATION and method IMPLEMENTATION**********//

HRESULT GetValue([in] BSTR bstrName, [out,retval] BSTR* pbstrValue);

STDMETHODIMP MyNativeClass::GetValue ( BSTR bstrName, BSTR* pbstrValue)
{
std::wstring strValue = GetValue( std::wstring( CW2W(bstrName) ),
true );
*pbstrValue = ::SysAllocString( strValue.c_str() );
return S_OK; }

//*******USAGE in C# code**********//

if (objNative.GetValue( "_Source" ) == string.Empty)
OR
m_SomeVariable.AssignVal( objNative.GetValue( "_Source" ) )

Now, will the String onject be collected by GC.

Regards,
Pawan Arya

Reply to this Message

TDC - 30 Aug 2006 13:29 GMT

Well, you didn't actually show your C# p/invoke declaration (assuming
you don't have an interop assembly), but it looks *highly* likely from
your C# usage that the BSTR will get marshalled correctly (copied into
managed memory and then freed).

Tom

> > The CLR will free the BSTR during the marshaling process if the
> > function has been declared correctly.
[quoted text clipped - 24 lines]
> Regards,
> Pawan Arya

Reply to this Message

Rate this thread:

Will SysAllocString allocation be GC'ed

Free Magazines