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date: Mon, 5 Jun 2006 21:37:42 +0200,
group: microsoft.public.platformsdk.com_ole
back
IEnumString next method question
Hi Everybody, i am stuck again with a newbie problem, but it's less
important since i have now a workaround, but it would be nice to have an
answer...
here is the problem, in my previous post, i exposed the IDL for the iriver
interface, one of the methods is dir :
[id(0x00000001), helpstring("method dir")]
HRESULT dir(IUnknown** ppenum);
I figured out that the object supports IEnumString with help of
QueryInterface.
Now i try to use the next method to fetch the first element of the
enumerator :
ULONG numreq;
ULONG numret;
wchar_t* element = 0;
hr = pUnkTest->QueryInterface(IID_IEnumString,(void **) &pTest);
if(SUCCEEDED(hr)) {
numreq = 1;
pTest->Next(numreq,&element,&numret);
wprintf(L"result: %u %s",numret,element);
}
It doesn't work as expected, i always get S_FAILED for hr and 0 for numret.
I informed myself a bit and it seems that the second parameter is a pointer
to a pointer of wide string (LPOLESTR) that is identical to wchar_t,
However, since the function can return multiple elements if numreq > 1, the
supplied second parameter, should be an array of pointers to wide strings,
right ??
Thank you again in advance.
date: Mon, 5 Jun 2006 21:37:42 +0200
author: Rod
Re: IEnumString next method question
Rod wrote:
> hr = pUnkTest->QueryInterface(IID_IEnumString,(void **) &pTest);
>
> if(SUCCEEDED(hr)) {
> numreq = 1;
> pTest->Next(numreq,&element,&numret);
> wprintf(L"result: %u %s",numret,element);
> }
>
> It doesn't work as expected, i always get S_FAILED for hr and 0 for
> numret.
This is normal. It just means the collection is empty - there's nothing
to enumerate.
> I informed myself a bit and it seems that the second
> parameter is a pointer to a pointer of wide string (LPOLESTR) that is
> identical to wchar_t, However, since the function can return multiple
> elements if numreq > 1, the supplied second parameter, should be an
> array of pointers to wide strings, right ??
Well, yes. But the function would never return more elements than you
ask for (as specified by the first parameter), and since you always ask
for one element, the issue is somewhat moot.
--
With best wishes,
Igor Tandetnik
With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925
date: Mon, 5 Jun 2006 15:50:13 -0400
author: Igor Tandetnik
Re: IEnumString next method question
"Rod" wrote in message
news:%237zhFeNiGHA.2268@TK2MSFTNGP04.phx.gbl...
> Hi Everybody, i am stuck again with a newbie problem, but it's less
> important since i have now a workaround, but it would be nice to have an
> answer...
>
> here is the problem, in my previous post, i exposed the IDL for the iriver
> interface, one of the methods is dir :
>
> [id(0x00000001), helpstring("method dir")]
> HRESULT dir(IUnknown** ppenum);
>
> I figured out that the object supports IEnumString with help of
> QueryInterface.
> Now i try to use the next method to fetch the first element of the
> enumerator :
>
> ULONG numreq;
> ULONG numret;
> wchar_t* element = 0;
>
> hr = pUnkTest->QueryInterface(IID_IEnumString,(void **) &pTest);
>
> if(SUCCEEDED(hr)) {
> numreq = 1;
> pTest->Next(numreq,&element,&numret);
> wprintf(L"result: %u %s",numret,element);
> }
>
> It doesn't work as expected, i always get S_FAILED for hr and 0 for
> numret.
> I informed myself a bit and it seems that the second parameter is a
> pointer to a pointer of wide string (LPOLESTR) that is identical to
> wchar_t, However, since the function can return multiple elements if
> numreq > 1, the supplied second parameter, should be an array of pointers
> to wide strings, right ??
That's correct.
You need to initialize numreq. The first parameter specifies how many
strings you want returned. Because it contains a garbage value, the Next()
method is returning S_FALSE. (There is no such HRESULT as S_FAILED).
Brian
date: Mon, 5 Jun 2006 12:52:34 -0700
author: Brian Muth
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