Calling COM method returning SAFEARRAY(BYTE)

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Graham Morris - 05 Oct 2005 14:25 GMT

Googling hasn't solved this little problem, so here goes:

I have a function in C++ which returns a safearray of bytes. I cannot
change this function, and I want to call it from C++. The IDL
looks like this:

interface IHash : IDispatch
{
[id(1)] HRESULT DoHash([in] BSTR strSource,[out,retval] SAFEARRAY(BYTE)*
abDestination);
};

I'd like to call it in C# with a simple

byte[] Dest = DoHash("A source");

However I get a "Specified array was not of the expected type" exception. I
suspect I might need to hand-craft an interface definition (rather than use
the interop) but I don't know how.

Reply to this Message

"Peter Huang" [MSFT] - 06 Oct 2005 07:31 GMT

Hi

Based on my test, it seems to be works at my side based on the IDE
generated Interop Assembly.
VC.NET C#.NET 2003

[C++]
[
    object,
    uuid("FBBDA07C-B48D-4B00-A24F-BEFD7EA52118"),
    dual,    helpstring("ITestHash Interface"),
    pointer_default(unique)
]
__interface ITestHash : IDispatch
{

    [id(1), helpstring("method DoHash")] HRESULT DoHash([in] BSTR strSource,
[out,retval,satype(byte)] SAFEARRAY** abDestination);
};

STDMETHODIMP CTestHash::DoHash(BSTR strSource, SAFEARRAY** abDestination)
{
    CComBSTR bst = strSource;
    CComSafeArray<byte> m_bts;
    unsigned int l = bst.Length();
    byte bt = l;;
    m_bts.Add(bt);
    m_bts.Add(2);
    *abDestination = m_bts.Detach();
    return S_OK;
}

Add reference to the COM above will get a interop assembly for use in C#
[C#]
[STAThread]
static void Main(string[] args)
{
    COMLib.ITestHash t = new COMLib.CTestHashClass();
    byte[] bt = (byte[])t.DoHash("Hello");
    Console.WriteLine(bt[0]);
    Console.WriteLine(bt[1]);
}

Best regards,

Peter Huang
Microsoft Online Partner Support

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Graham Morris - 06 Oct 2005 15:39 GMT

You are using attributed C++: I had a C++ component with a separate IDL
file. The C++ component works fine with a VB6 client.

Anyway I've programmed round this problem now. (I've done what I wanted
another way). Thanks for the reply.

> Hi
>
[quoted text clipped - 47 lines]
> This posting is provided "AS IS" with no warranties, and confers no
> rights.

Reply to this Message

"Peter Huang" [MSFT] - 07 Oct 2005 03:12 GMT

Hi

Thanks for your quickly reply!
And I am glad that you have resolved it.

Best regards,

Peter Huang
Microsoft Online Partner Support

Signature

Get Secure! - www.microsoft.com/security
This posting is provided "AS IS" with no warranties, and confers no rights.

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Calling COM method returning SAFEARRAY(BYTE)

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