::SysFreeString() crashing in WINDOWS2008 only

Question

I have a COM code where i use BSTR.

In that the application crashes when using ::SysFreeString()

However the same works in WINDOWS2003, WIN7, WINXP etc.

Any idea on what is causing the problem or what could be wrong. Sample code is as below

class CFoo::IUser 
{  
BSTR UserName; 

}
HRESULT CBar::FooMethod(VARIANT *vOut) 
{
//create interface, variant and fill the object.

BSTR bstrname = ::SysAllocString(_T("Username")); 
//use bstrname to fill interface structure.
//finished using now deallocate memory

::SysFreeString(bstrname); // crashing here only in windows 2008 R2 

}

One minor issue: whether `SysAllocString` uses wide characters or not is not controlled by the UNICODE macro, so using the `_T()` macro with it isn't correct (under normal circumstances, you should always use wide characters, and it you want to use a macro it should be `OLECHAR()`). Beyond that, we're going to have to see more code to diagnose this. Can you produce a small, compilable example that exhibits the problem? — Sven, Feb 28 '12 at 12:16
There is nothing more in actual code. Just i will use that variable bstrname and assign it to another member variable of an interface. — ckv, Feb 28 '12 at 12:17
But this code on its own has no problems (unless you're compiling without UNICODE, due to the macro issue I mentioned) and won't cause a crash. You can't expect us to magically divine what the actual problem is. Unless you can show us a complete example that reproduces the problem, there's nothing we can do. — Sven, Feb 28 '12 at 12:20
@ckv, the question looks like a duplicate for [this one](http://stackoverflow.com/questions/9467004/freeing-a-bstr-using-sysfreestring-more-platform-dependant) — Igor Chornous, Feb 28 '12 at 12:26
@kids_FoxYeah i Dont deny. But that answer didnt help me. So looking for more anwsers from experts. — ckv, Feb 28 '12 at 12:31
Shows us the code that assigns the BSTR to the interface member, and show us how that interface stores the BSTR and uses it. Is it making a copy? Because if not, you might be using a BSTR after freeing it, and Windows caches BSTR instances so you *might* get away with that until your luck runs out (in this case, if Windows changed its caching behavior). — Sven, Feb 28 '12 at 14:31

score 3 · Accepted Answer · answered Feb 28 '12 at 12:36

I would suggest to stop using the raw forms like BSTR. Instead use wrapper classes like _bstr_t which encapsulates the raw BSTR pointer. The class manages resource allocation and deallocation through function calls to SysAllocString and SysFreeString and other BSTR APIs when appropriate.

::SysFreeString() crashing in WINDOWS2008 only

1 Answers1