Re: using arrays as function parameters, with c#

"Alexander Nickolov" <>
Tue, 25 Apr 2006 09:49:21 -0700
FWIW, this is a known quirk of safe arrays - you have to use
an extra indirection for [in] safe array parameters.

Alexander Nickolov
Microsoft MVP [VC], MCSD

"fabien bole-feysot" <> wrote in
message news:Ojaoj1EaGHA.3740@TK2MSFTNGP03.phx.gbl...

I just found my mistake : if I use SAFEARRAY* in the idl, then my C++
function should take a SAFEARRAY** parameter...
With this change, I now correctly see my array in my ATL function !

But it does not seem to work, if I use SAFEARRAY in the idl, and
SAFEARRAY* in the c++ function... So I'll stick to the SAFEARRAY** for the
Thanks for your help !

"fabien bole-feysot" <> a ?crit
dans le message de news: %230mmsvEaGHA.4424@TK2MSFTNGP05.phx.gbl...

Thanks Brian, so I moved to unattributed code, and used the SAFEARRAY the
way you explain.
I now see, in c#, my funciton with a parameter of type 'ref
System.Array'. Looks good to me
But when I try to call the function with a System.Array that holds 2
elements, my ATL function get called, but with invalid values...
The SAFEARRAY I receive has a cdims of 44960, a cbElements of 0, null
data, a fFeatures of 33, a low bound of 10687108 ...
I suppose there is still something I don't do the right way, if you could
please have a look at my code...
thanks a lot for your help

Here is my code :
in the idl file :
helpstring("IPs3Bridge Interface"),
interface IPs3Bridge : IDispatch {
 [id(1), helpstring("method enumTargets")] HRESULT
enumTargets([in]SAFEARRAY(LONG)* _pArray);
[ version(1.0), uuid(1C1CEE99-298A-496F-A3A8-F9B67BB27AA0),
helpstring("ps3_bridge 1.0 Type Library") ]
library ps3_bridge

 helpstring("Ps3Bridge Class")
coclass Ps3Bridge {
 interface IPs3Bridge;

in the h file :
// IPs3Bridge
dual, helpstring("IPs3Bridge Interface"),
__interface IPs3Bridge : IDispatch
 HRESULT enumTargets(SAFEARRAY* _pArray);

// Ps3Bridge
helpstring("Ps3Bridge Class")
class ATL_NO_VTABLE Ps3Bridge :
public IPs3Bridge


HRESULT FinalConstruct();
void FinalRelease();


 STDMETHOD(enumTargets)(SAFEARRAY* _pArray);

in the cpp file :
STDMETHODIMP Ps3Bridge::enumTargets(SAFEARRAY* _pArray)

in the c# file :
     ps3_bridge.Ps3BridgeClass bridge = new ps3_bridge.Ps3BridgeClass();
     System.Array array = System.Array.CreateInstance(typeof(Int32),2);
     int[] array2 = new int[2];
     array2[0] = 5;
     array2[1] = 10;
     bridge.enumTargets(ref array);

"Brian Muth" <> a ?crit dans le message de news:

"fabien bole-feysot" <> wrote in
message news:uVEFZD7ZGHA.4424@TK2MSFTNGP02.phx.gbl...

I have a COM Object MyComObject, and I would like to add a method that
take an array of long as a parameter.
The purpose of this method is to receive an already-allocated array of
long, and to fill it : void fillArray( long* first, int size) or
something like that.

This method is to be called from a c# code, so I would like it to be
seen as fillArray( long[] ) from my csharp module.
example of the way I would like to use it in c# :

long[] myArray = new long[10];

How can I define this method in my COM object ? (All I need is the
exact declaration to put in the __interface MyComObject : IDispatch
section, and the corresponding C++ declaration for htis method

I tried to 'play' with SAFEARRAY, but I could not find a way to have it
understood by the compiler...

I can certainly provide you with a solution, but let me preface my
answer by stating that I do not work with attributed ATL. Visual Studio
2003 was very buggy with attributed ATL, and I'm shy to use it in Visual
Studio 2005 as well. So I will show you the unattributed solution. In
fact, most experts in this forum avoid attributed ATL as well; I suggest
you do the same.

Unfortunately for you, marshaling C# types of long[] is quite involved,
and I don't recommend it. You are much better off marshaling an Array
instead. You can use variables of type long[] if you like, but copy them
into an Array first.

Your IDL (unattributed ATL) can look like this:

[id(1), helpstring("method FillArray")] HRESULT FillArray([in, out]

Note it is not necessary to pass the length of the array as a separate
parameter. That information is embedded in the safearray itself.
To call this from C#, see below:

MyArrayLib.ArrObjClass c = new MyArrayLib.ArrObjClass();
Array arr = Array.CreateInstance (typeof (Int32), 2); // create a two
element array
arr.SetValue (0, 0); // set some values
arr.SetValue(2, 1);
c.FillArray(ref arr);



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