Why does my dll not work for VBA calling?

[rock31]

I have programed a DLL, it compiles fine from C++ express edition 2008. But I can not call it from VBA.
The following is the code, hope anyone can help me.

This is testdll2_for_vba.h

 
#ifndef DLL3_H
#define DLL3_H
 
#ifdef DLL3_EXPORTS
    #define DLL3_API __declspec(dllexport)
#else
    #pragma message("automatic link to DLL3.LIB")
//    #pragma comment(lib, "DLL3.lib")
    #define DLL3_API __declspec(dllimport)
#endif
 
 
 
// This class is exported from the Test.dll
class DLL3_API CTest 
{
public:
    CTest(void);
    // TODO: add your methods here.
};
 
extern DLL3_API int nTest(const int& m);
 
 
double DLL3_API __stdcall  testplus (const double& a, const double& b);
 
 
#endif //DLL3_H
 
 

This is dllmain.cpp

// dllmain.cpp : Defines the entry point for the DLL application.
#include "stdafx.h"
#define TEST_EXPORTS                     // <===  ADD THIS LINE
//#include "testdll2.h"
#include "testdll2_for_vba.h"
BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}
 
 

This is my source code:

// testdll2.cpp : Defines the exported functions for the DLL application.
//
 
#include "stdafx.h"
 
int nTest(const int& m){
    return m;
}
 
double testplus (const double& a, const double& b){
    return a+b;
}
 
 

This is my VBA code:

 
Public Declare Function testplus Lib _
    "C:\Documents and Settings\Owner.SpiritBirdV1\My Documents\Visual Studio 2008\Projects\testdll2\Debug\testdll2.dll" (ByRef a As Double, ByRef b As Double) As Double
 
 
Sub test()
 
End Sub
 
Function bs_test(s As Double, k As Double, r As Double, sigma As Double, time As Double) As Double
'bs_test = option_price_call_black_scholes(s, k, r, sigma, time)
bs_test = testplus(s, k)
End Function
 
 

Thank you very much.

I read some articles about create DLL from VC++, that requires .def to alias the exported symbols. But I failed to find where to create .def in c++ express edition 2008. what should I do to fix the problem?

Thanks again

[weaknessforcats]

The problem you have is that C++ has function overloading.

Since the same function name with different arguments is acceptable, the C++ compiler decorates (mangles) the function name to a unique entitity that reflects the arguments and their type. Please don't ask how this is done.

The effect is that

void MyFunction(int);

becomes

?YAXX2GHQ (I made this up).

What's in the dll is ?YAXX2GHQ and VBA is looking for MyFunction and it's never found.

Use a .DEF file. It's just a text file. Here is an example:

;BEGIN ADLL.DEF FILE
;This DEF file is required becuase the argument to GetProcAddress()
;for the function is a C-string and it will never be equal to the
;C++ mangled name for the function
;This DEF file maps the mangled name to a name that can be used with GetProcAddress()
;Note also: Change project settings in Visual Studio to send the LINK this def file.
;Visual Studio.NET: Project Properties/Linker/Input/Module Definition File/...Path to the def file\Adll.def
LIBRARY ADll 
EXPORTS 
;Exported Name    C++ Mangled Name
AreaOfSquare   =  ?AreaOfSquare@@YGHHH@Z
DisplayFromDll =  ?DisplayFromDll@@YGXXZ
;END DEF FILE 
 

The lines beginning with semi-colons are comments.

Note the comment about adding the path to your DEF file to your VC project.

Let me know what happens.