c++ dll and Visual Basic 5.0

I'm trying to write a dll that will work in VB 5.0.
I just tried to write a simple "hello world" function in
the dll and it worked when I called the dll from another
c++ program, but not vb.  

Basically, here is my code.

#define DLL_EXPORT __declspec(dllexport)

extern "C"
DLL_EXPORT int TestText(char* out)
 strcpy(out, "Hello world");
 return 1;

vb 5.0 - form1
Private Sub Command1_Click()
    Dim Text2 As String * 20
    Dim ret As Integer
    ret = TestText(Text2)
    MsgBox Text2
End Sub

vb5.0 module1.bas
Declare Function TestText Lib "mime.dll" (ByRef sHold As String) As Long
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Just a guess.  Basic strings and c strings are different.  Basic stores a count byte before the text.  c strings are zero delimited.
Strings in VB5 are not represented as they are in Microsoft C++. In VB5, strings are stored in a structure that is invisible to the programmer called a VARIANT. The VARIANT represents a variant union, and the type in the union to represent string on the C++ side is called BSTR. See the Microsoft help on BSTR. One has to allocate and de-allocate BSTR strings as one would normal memory.

The C++ program should look something like:

DLL_EXPORT int TestText (BSTR *pbstrOut)
   *pbstrOut = SysAllocString (L"Hello World");
 if (*pbstrOut == NULL)
    return 0; // didn't get any space for string.
   return 1;

BSTR is a built-in Microsoft type the prefixes string with the length AND zero  byte terminates them.  There are a number of "SYS..." functions to manipulate BSTR's. SysAllocString allocates space for the argument, and does a string copy of the argument to the allocated space.

I believe your VB program should work as is.  

Good luck, MK.
ivanhAuthor Commented:
I tried what you said, but VB keeps telling me
  Error '49':  Bad DLL calling convention

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Try changing the ByRef keyword in your Declare statement for the string parameter to a ByVal.  This is how you deal with char * paramaters (and it does not pass by val, but converts strings to/from C ASCIIZ still passing ByRef)

ivanhAuthor Commented:
So you are saying to use my first code and just change
from byref to byval?  I tried that and still got the 49 error.
I also tried with the modified code and recieved the same 49
what compiler are you using?  I know that newer microsoft compilers will dork with the C function name appended and @ and a number (I think the number of bytes on that paramater stack?). I don't have a C++ compiler here rite now, so I can't figure it out.  I think maybe the calling convention for your function may be incorrect. Sorry I can't give you an exact answer..it's been a few years since I wrote DLL's for VB and things have changed some, at least in MSVC

ivanhAuthor Commented:
I'm using MSVC 5.0.  
Error 49 indicates that you're using the wrong calling convention for your function.

Your function should not be declared extern "C" (which, by the way, should rather be __cdecl) but __pascal

If you're using VC++4.2 or above, use WINAPI instead of __pascal

So the prototype should read
DLL_EXPORT __pascal int TestText(LPSTR *p)

And your VB declaration should be

Declare Function TestText Lib "mime.dll" (ByVal sHold As String) As Long
Hope this helps,

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ivanhAuthor Commented:
Actually, the first answer was right, but Groby's answer is
really the one I was looking for.  
My real big problem was that I didn't have a def file.
I also found out out that doing a ByVal, you can use LPSTR and
if you are doing a ByRef you have to use BSTR.  But this
is what you guys demonstrated in your code, but I just didn't
make the connection until I started reading some docs.  
Thanks all for the help.  I learned a lot!
Hi, I'm trying to make a dll and I'm looking for some help with this. I tried what you say here but didn't work, this is how I declared the function in VB:

Private Declare Function copystrings Lib "O:\mypath\usuarios.dll" (ByVal Dest As String, ByVal Source As String)

This is my dll code:

LIBRARY usuarios.dll
copystrings               @1

// Usuarios.cpp : Defines the entry point for the DLL application.

      A2CW       (LPCSTR)  -> (LPCWSTR)
      A2W        (LPCSTR)  -> (LPWSTR)
      W2CA       (LPCWSTR) -> (LPCSTR)
      W2A        (LPCWSTR) -> (LPSTR)

//#include <afxpriv.h>
#include "stdafx.h"

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <windows.h>
#include <wchar.h>
#include <winerror.h>
#include <lmcons.h>
#include <lmaccess.h>
#include <lmapibuf.h>
#include <ole2.h>

#define DllExport __declspec(dllexport)

                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
    return TRUE;

DllExport PASCAL copystrings( char* dest, char* src )
//      wcscpy(dest,src);
      return 1;

Can you tell me what's wrong, please?

Thanks in advanced.

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