Board index » delphi » Can anyone please help me code the IEnumSTATPROPSETSTG Next method?

2008-08-02 06:02:01 PM
delphi270
Can anyone please help me in coding an implementation of the
IEnumSTATPROPSETSTG Next method?
MSDN ( msdn.microsoft.com/en-us/library/aa379213(VS.85).aspx )
describes it as follows:
The Next method retrieves a specified number of STATPROPSTG structures,
that follow subsequently in the enumeration sequence.
HRESULT Next([in] ULONG celt, [out] STATPROPSTG* rgelt, [out] ULONG*
pceltFetched);
Parameters
celt The number of STATPROPSTG structures requested.
rgelt An array of STATPROPSTG structures returned.
pceltFetched The number of STATPROPSTG structures retrieved in the
rgelt parameter.
QUESTION 1
My implementation stub is as follows. It compiles OK, but fails with a
memory access fault when I try to assign something to the array. Can
anyone please tell me what I am doing wrong?
++++
function Txx.IEnumSTATPROPSETSTG_Next(celt: ULONG; out rgelt;
pceltFetched: PULONG): HResult;
type
TStatPropSetStgArray = array of TStatPropSetStg;
PStatPropSetStgArray = ^PStatPropSetStgArray;
var
lArray: PStatPropSetStgArray;
hnd: THandle;
begin
// get some memory
hnd := GlobalAlloc(GHND, celt * sizeof(TStatPropSetStg));
// lock it
lArray := GlobalLock(hnd);
// try to use the array -- FAILS !!
lArray^[0].fmtid := ... <= Access Violation!!
++++
QUESTION 2
There is a discrepancy between the wy that Delphi declares the interface
in ActiveX and the way Microsoft describes it on MSDN
Delphi ActiveX declaration:
function Next(celt: ULONG; out rgelt; pceltFetched: PULONG): HResult;
stdcall;
Microsoft declaration:
HRESULT Next([in] ULONG celt, [out] STATPROPSTG* rgelt, [out] ULONG*
pceltFetched);
Because of this, I don't know what is the correct way to return the data
array in the Delphi defined untyped out parameter "rgelt". My code is as
follows. Is it correct?
// return the out parameter
PStatPropSetStgArray(rgelt) := lArray;
Thanks in advance...
 

Andrew Fiddian-Green writes: