In Delphi automation server, how to return a string array to client (string[])

Question

I am developing an automation server in Delphi and a couple of properties need to return arrays of strings. The specification asks for (with examples in 3 languages):

C# 
string[] Names { get; }

Visual Basic 
ReadOnly Property Names As String()
    Get

Visual C++ 
property array<String^>^ Names {
    array<String^>^ get ();
}

I have tried many way to do this an am stuck including SafeArrays and Variants as the RIDL type. My latest attempt (so I have at least one example) is:

function TFW.Get_Names: OleVariant; safecall;

var
  I : integer;
  NumFilters:integer;
  Filters:FieldsType;
  V:OleVariant;

begin
  NumFilters:=SplitFields(Filters,FilterNames,',','"');

  V := VarArrayCreate([1,NumFilters], VT_BSTR);

  for I := 1 to NumFilters do
    V[I]:=Filters[I];

  Get_Names:=V;  
end;

The client application in this case complains with the error:

"Unable to cast object of type 'System.String[*]' to type 'System.String[]'."

Thanks in advance!

I found the problem - the type cast did not like the array not being zero-based, changing that and the problem is fixed. — Dave Lane
– Dave Lane, Commented Nov 19, 2017 at 21:40

Dave Lane · Accepted Answer · 2017-11-19 21:45:05Z

2

The solution is to create the variant array zero-based, instead of 1...X):

V := VarArrayCreate([0,NumFilters-1], VT_BSTR);

  for I := 0 to NumFilters-1 do
    V[I]:=Filters[I+1];

Case closed!

answered Nov 19, 2017 at 21:45

Dave Lane

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1 Comment

Ondrej Kelle Over a year ago

You could also simply use a WideString array which Delphi would convert automatically to a zero-based variant array of BSTR.

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