Re: How to get a variant returned from a c++ function in vb.net?

On 17 Nov 2005 01:39:40 -0800, "Thomas W" <twtemp@xxxxxx> wrote:

> This function (which I can't change) executes a SQL query and returns a
> single value - whatever the query asks for: integer, string, double
> etc.

Is there a reason why you can't use .Net data objects and execute the query
directly from VB.Net code? It sounds like ExecuteFunction does exactly the
same as the ExecuteScalar method of a .Net SqlCommand object.

Imports System.Data.SqlClient
[...]
Dim cn As New SqlConnection(ConnectionString)
cn.Open
Dim cmd As New SqlCommand("Your query", cn)
Dim x As Object = cmd.ExecuteScalar()


> Private Declare Auto Function ExecuteFunction Lib "database.dll" ( _
> ByVal sSQL As Char) As Object

I could be wrong on some or all points, but I see more than one problem
here.

First, I think you'll have to pass the query differently: Char is a single
character, not a pointer to a string as the function expects.
I've never tried, but I think it will pass the ASCII value of the first
character of your query instead of a pointer to the string.

Second, but I'm really not sure here, I think "auto" assumes that the
function exists in ExecuteFunctionA and/or ExecuteFunctionW variations in
the DLL (as most API functions that take strings do), use either 'ansi' or
'unicode' depending on what the DLL expects. Again, I've never tried, but
I think "auto" may append either an A or a W to the function name.

Third, I don't know if AsAny works on return values, but try this:


Private Declare Ansi Function ExecuteFunction Lib "database.dll" ( _
ByVal sSQL As String) As <MarshalAs(UnmanagedType.AsAny)> Object


I think it will tell you that you can't use AsAny on a return value though.
Even if you can, the error message makes me expect you'll still get the
same error because returning variants is really not supported.
.

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