DLL's Compatibility

[cheery_poori]

Hello,

I have developed a DLL in VC++, i want to use it in VB and VB.net.. When i try to use the DLL in vb it is giving Bad DLL Calling Convention. I changed the Calling Convention to __stdcall from __cdecl* Code Generation option in C/C++ tab in Project Settings. I will be able to use the DLL compiled with __stdcall in VB but if i use the same DLL in VC++ againg, it will give error unresolved external symbol __imp__('Function Name'). Can anybody please help me..its urgent

Thanks in advance,
Poornima.

[HoM]

if you declare a function _stdcall, VC will not have any problems calling it. ACtually: all win APIs are _stdcall, so ... there should not be a problem.

just make sure, that the dll and the program consuming the dll use the same header.

regards
HoM

[Krishnaa]

Hello,

I have developed a DLL in VC++, i want to use it in VB and VB.net.. When i try to use the DLL in vb it is giving Bad DLL Calling Convention. I changed the Calling Convention to __stdcall from __cdecl* Code Generation option in C/C++ tab in Project Settings. I will be able to use the DLL compiled with __stdcall in VB but if i use the same DLL in VC++ againg, it will give error unresolved external symbol __imp__('Function Name'). Can anybody please help me..its urgent

Thanks in advance,
Poornima.

Try using

extern "C" __stdcall void MyExportedFunction()
{
}

[cheery_poori]

Hi..,

I have tried both of the above mentioned ideas..but it is still giving the same problem.

[Krishnaa]

Is the function signature ( like int myfunction(); ) added to the project where you are using it ?

What is the function signature there ?

[cheery_poori]

Hi,

My function signature lokks like below...
CRF_U_API int __cdecl POn_CRF(char * sR);

[Krishnaa]

But you have modified it in DLL to have __stdcall.

The function signature has to be same everywhere (in DLL and where you use/call it).

Make it as,

CRF_U_API int __stdcall POn_CRF(char * sR);

[cheery_poori]

If i use __stdcall will it work in VC++?

[Krishnaa]

Yes.....

__stdcall is just a calling convention, it not only for VB. VC++ (rather C/C++) programs understand a lot of other function calling conventions too but VB assumes external functions to be __stdcall.

[cheery_poori]

Hello Krishnaa,

My program is working..thanks

Thanks & Regards,
Poornima.

[Krishnaa]

Good !

[cheery_poori]

Hello Krishnaa,

I have one more problem.. in my dll i am returning a char* array.., in vb i am not able to get this return parameter.. My function is as below...

'Public CRF_U_API char * __stdcall GetCName( int CType );
Public Declare Function GetCName Lib "Crf.dll" _
(ByVal CType As Integer) As Byte

Thanks & Regards,
Poornima.

[Krishnaa]

Declare VB signature as

Public Declare Function GetCName Lib "Crf.dll" (ByVal CType As Integer) As String

[cheery_poori]

Hello Krishnaa,

I have tried using String as return parameter..but it gives 'memory could not read' error and abruptly closes my application.

Thanks & Regards,
Poornima.

[Krishnaa]

You will need to use BSTR as return type instead of Char* in VC DLL,
like this,

CRF_U_API BSTR __stdcall GetCName( int CType );

{
   char* lpszText = "Test";
   printf("char * text: %s\n", lpszText);
   BSTR bstrText = _com_util::ConvertStringToBSTR(lpszText);
   return bstrText ;
}