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DLL API String return value query

Posted on 2004-09-27
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Last Modified: 2010-05-02
Hi,
We are trying to access the following API , present in a particular DLL :
API defined in C:
short EXPORT TblGetValue(char *Param1, char *Param2, void *RetValue)

This API returns the value in the variable 'RetValue'
For Example if we need a value which satifies the conditions passed in Param1 and Param2 the value will be returned in RetVal

Stat = TblGetValue('TESTTBL','TESTKEY',RetStrValue)
The value is returned in the 'RetStrValue' parameter.

Declaration in VB:
public declare function TblGetValue LIB "TABLE32.DLL" (ByVal TblId As String, ByVal KeyId As String, ByRef Value as String) As Integer.

When we try to access this in VB we get a following message :

"Variable uses an automation type not supported in Visual Basic."

Please can anyone let us know the solution to this issue. We are using VB6.0 on Windows 2000.

Thanks

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Question by:d_lalit
6 Comments
 
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Expert Comment

by:EDDYKT
ID: 12159149
Try


ByRef Value as any


or


ByRef Value as Variant
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Expert Comment

by:fds_fatboy
ID: 12159192
Surprisingly I think you have to call it with a ByVal instead of a ByRef
i.e.
public declare function TblGetValue LIB "TABLE32.DLL" (ByVal TblId As String, ByVal KeyId As String, ByVal Value as String) As Integer

This is to do with VB's string pointer handling. You create a buffer and pass the value of the pointer to the start of that buffer. Also, you'll need to fill the Value buffer before you call it.

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Expert Comment

by:Erick37
ID: 12159818
This may apply:

PRB: Error Compiling VB5 Project Using LPVOID in Type Library
http://support.microsoft.com/default.aspx?scid=kb;en-us;193016

Also, if the C DLL is passing char*, then I believe you must receive it into a byte array, then use the StrConv function to convert it back to inicode.
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modulo
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