Calling a C++ DLL which returns a String

[Vorreiter Johann (IFDA)]

Hi,

following problem:
in my EXCEL VBA-code I try to call a function from a C++ DLL which has the
following declaration:

long TestFunc( char* TestStr );

In this function the TestStr is modified.

VBA-code:

Declare Function TestFunc& lib "TestDll.dll" ( VBAString as String )

Dim DummyStr as String
DummyStr = "this is a test"
ret = TestFunc( DummyStr )

BUT, after calling TestFunc EXCEL crashes...
As long as I don't touch the string in the C++ funtion everything is ok.

Any other idea how to return a string from a DLL?

Thanks,

Johann

[mct]

I don't know how your DLL was constructed; 'normal' Win32, as a Static
Library, or via MFC. But there is another way to import C-functions in
VB(A). This is how I get an Int.

DLL.DLL:

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

#include "stdafx.h"

UINT DLL_Function_Name();

BOOL APIENTRY DllMain( HANDLE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
return TRUE;
}

UINT DLL_Function_Name()
{
return 12345;
}

Then, DLL.DEF:

EXPORTS
DLL_Function_Name

Finally, in Excel VBA:

Option Explicit

Public Declare Function LoadLibrary Lib "kernel32" Alias "LoadLibraryA"
(ByVal lpLibFileName As String) As Long
Public Declare Function FreeLibrary Lib "kernel32" (ByVal hLibModule As
Long) As Long
Public Declare Function GetProcAddress Lib "kernel32" (ByVal hModule As
Long, ByVal lpProcName As String) As Long
Public Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA"
(ByVal lpPrevWndFunc As Long, ByVal hWnd As Long, ByVal Msg As Long, ByVal
wParam As Long, ByVal lParam As Long) As Long

Public Function DoDLLFunction() As Integer
Dim X As Long
Dim Y As Long
X = LoadLibrary("C:\Excel Projects Usenet\DLL2.DLL")
Y = GetProcAddress(X, "DLL_Function_Name")
MsgBox Y
DoDLLFunction = CallWindowProc(Y, ByVal 0&, ByVal 0&, ByVal 0&, ByVal
0&)
FreeLibrary X
End Function

...will give 12345 in the ActiveCell by entering =DoDLLFunction()
Maybe you can experiment with this.

hans

Hans

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[Vorreiter Johann (IFDA)]

Thanks Hans,

this works fine, but what to do if I want to return a string instead of an
UINT??

Regards,

Johann

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