Hi!

I'm relative new to Visual Basic, but pretty comfortable with C/C++.
I want to call a C/C++ generated DLL from within a VB ActiveX Control.
More precisely, I want to give the DLL the pointer of a callback-
function
and the DLL calls this function in the ActiveX Control.

While I managed it to set up the callback-mechanism, I have problems
with
the data. The C/C++ DLL calls the VB ActiveX function with a C/C++
struct
like this:

typedef struct tagDATA {
    long Number1;
    long Number2;
    char String1[100];
    char String2[100];

The prototype in C/C++ looks like this:

void ActiveXCallbackFunction(LPDATA lpData);

I converted this to VB:

Public Type DATA
    Number1                       As Long
    Number2                       As Long
    String1                       As String * 100
    String2                       As String * 100
End Type

The Callback-Function in the VB Control looks like this:

Public Sub CallbackFunction(ByRef lpData As DATA)
    MsgBox CStr(lpData.Number1) ' Output: ok
    MsgBox CStr(lpData.Number2) ' Output: ok
    MsgBox lpData.String1       ' Output: "???"
    MsgBox lpData.String2       ' Output: "???"
End Sub

The problem is, that the numbers are transmitted correctly,
but the strings are a mess, displaying "?" and spaces.

I have'nt found a way to do it in the documentation,
so I hope someone of you VB-pro's can help me on this.

TIA
Jochen

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Jochen,

This is most likely a ANSI/Unicode issue. The C++ code sends ANSI
characters to your VB function, which expects Unicode characters in
the structure. Try it like this instead:

Public Type DATA
    Number1                       As Long
    Number2                       As Long
    String1(0 To 99)              As Byte
    String2(0 To 99)              As Byte
End Type

Public Sub CallbackFunction(ByRef lpData As DATA)
    MsgBox CStr(lpData.Number1)
    MsgBox CStr(lpData.Number2)
    MsgBox StrConv(lpData.String1, vbUnicode)
    MsgBox StrConv(lpData.String2, vbUnicode)
End Sub

Mattias

____________________________________________

    http://hem.spray.se/mattias.sjogren/
              Docendo discimus

Yes, it seems this was a unicode-problem. I changed my code according to
your example and everything works fine now. Thank you,

Jochen

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