Problem returning empty Safearray from OLE Component

Kevin Godden Mon, 16 Oct 2006 07:21:08 -0700

Hi all,

I hope that somebody can help me with a problem that I am having while returning a 1D Safearray to a Perl client from an OLE component, everything is OK when the array has some elements, but if the array is empty I get the following error:

Win32::OLE(0.1704) error 0x8002000b: "Invalid index"

I am using Active State Perl Version 5.8.8, Build 819. I am testing under windows XP, service pack 2, and I am building my OLE interface with Visual Studio 6, SP6.

I have created a cut-down COM object to test the problem, its interface supports IDispatch and is OLE Automation compatible. In the IDL file the test method is declared as:

[id(1), helpstring("method GetArray")] HRESULT GetArray([in] int elementCount, [out, retval] VARIANT* pV);

This method returns a SAFEARRAY in a Variant, the elementCount argument indicates how many elements should be placed in the array before it is returned.

This is how GetArray() is defined, it creates a Safearray of type VT_I4:

STDMETHODIMP CTestOutArray::GetArray(int elementCount,

VARIANT *pV)
{
V_VT(pV)= VT_ARRAY | VT_I4;

   SAFEARRAYBOUND saBound;
   saBound.lLbound = 0;
   saBound.cElements = elementCount;

SAFEARRAY* pA = SafeArrayCreate(VT_I4, 1, &saBound);

V_ARRAY(pV) = pA;

   if (elementCount > 0)
   {
    long val = 1234;

    for (long i = 0; i< elementCount; i++)
     SafeArrayPutElement(pA, &i, &i);
   }

return S_OK;
}

I have got rid of any error checking code etc. to make it a bit easier to read...

When I call this from Perl with elementCount > 0, everything works OK, but when I call it with elementCount == 0 I get the 'Invalid Index' error.

Here is the client Perl Code:

use strict;

use Win32::OLE qw(in with);

$Win32::OLE::Warn = 3;

my $test = Win32::OLE->new('PerlOutArrayTest.TestOutArray', 'Quit') or die "Couldn't create object";

my $arr = $test->GetArray(1); # Works OK

my $second_arr = $test->GetArray(0); # Throws an error

Can anybody spot if I am doing something wrong? Should Perl work OK when an OLE method returns an empty Safearray, or should I just expect it to throw this error when the array is empty?

It's all a bit of a pain as I sometimes need to return an empty array as part of normal operation, and I don't want to have to add loads of nasty extra code handle the situation as an error...

Any help would be greatly appreciated, thanks for reading!

Kevin Godden.

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Problem returning empty Safearray from OLE Component

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