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From: DHarray on 6 Nov 2006 04:41
Hello,

I want to enumerate my Band Objects with the use of IBandSite because i
need a special band id for my application:

_COM_SMARTPTR_TYPEDEF(IBandSite, __uuidof(IBandSite));

CoInitialize(NULL);

// ...

IBandSitePtr bs;
bs.CreateInstance(CLSID_TrayBandSiteService);
if (bs)
{
LONG count = bs->EnumBands(UINT(-1), 0);

printf("%i",count); // -2147023116
}

// ...

CoUninitialize();



Any idea why EnumBands returns a wrong value? MSDN said that the first
value has to be "-1" to get the number of bands. thanks for any help
From: Stuart Redmann on 6 Nov 2006 06:09
DHarray wrote:

> Hello,
>
> I want to enumerate my Band Objects with the use of IBandSite because i
> need a special band id for my application:
>
> _COM_SMARTPTR_TYPEDEF(IBandSite, __uuidof(IBandSite));
>
> CoInitialize(NULL);
>
> // ...
>
> IBandSitePtr bs;
> bs.CreateInstance(CLSID_TrayBandSiteService);
> if (bs)
> {
> LONG count = bs->EnumBands(UINT(-1), 0);

Try:
DWORD Dummy;
HRESULT hr = bs->EnumBands ((UINT)-1, &Dummy);

and add

if (!SUCCEEDED (hr))
{
// Some error handling.
}

>
> printf("%i",count); // -2147023116

Use the errlook tool that ships with Visual Studio to look up this error
code. It will tell you that you have passed a NULL pointer for a
top-level pointer, which is not allowed.

> }
>
> // ...
>
> CoUninitialize();
>
> Any idea why EnumBands returns a wrong value? MSDN said that the first
> value has to be "-1" to get the number of bands. thanks for any help

Though the second parameter to EnumBands will be ignored, you cannot
pass a NULL pointer to the method (the call is made through a proxy
which check that all top-level pointers are valid).

This example shows that even Microsoft can create really, really awful
APIs. It would have been quite easy to introduce a method
HRESULT IBandSite::GetNumberOfBands ([out, retval] int* RetVal),
instead of this ugly 'When you pass a minus one as _unsigned int_
parameter!!!, you'll get this, else you'll get that humdrum. Take this
as an example of how to _not_ create an API.

Regards,
Stuart
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