DLL's Compatibility

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.

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

Quote:

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Originally Posted by 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.

---

Try using

Code:

---

extern "C" __stdcall void MyExportedFunction()
{
}

---

Hi..,

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

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

What is the function signature there ?

Hi,

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

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,

Code:

---

CRF_U_API int __stdcall POn_CRF(char * sR);

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

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.

Hello Krishnaa,

My program is working..thanks

Thanks & Regards,
Poornima.

Good ! :cool:

:wave:

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.

Declare VB signature as

Code:

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

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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.

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

Code:

---

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 ;
}

---

ConvertStringToBSTR is declared in comutils.h.

You can use ConvertBSTRToString to get your char* back from BSTR if needed in C++ application.

Hello..,

I have tried using BSTR but i want my DLL to be compatible in C, Borland C++, VB, VC++, Java and .Net..so if i use BSTR then i wont be able to use it in basic 'C'., is there any other way to do so...

Quote:

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Originally Posted by cheery_poori

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...

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Perhaps the standard way of exposing functionality developed in C++ to an automation client like VB is by using COM. i.e. Making your class Automation-COM compliant will allow you to use functionality using standard VB syntax, like this -

Code:

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Set objectName = CreateObject ("YourDllName.ClassName")

objectName.DoSomething ()

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Further read:

• Post + Sample: Invoking functionality in a C++ COM DLL from VB Script Client
• Post + Sample: Invoking functionality in a C++ COM DLL from VB.NET Client

The approach you have chosen so far is to use the export functionality of a "C" style DLL - a relatively outdated mechnism when compared to DLLs programmed in C++ that are COM compliant.

COM compliance brings with it the advantage of adhering to standards designed for cross-language programming capabilities.

Quote:

---

Originally Posted by cheery_poori

I have tried using BSTR but i want my DLL to be compatible in C, Borland C++, VB, VC++, Java and .Net..so if i use BSTR then i wont be able to use it in basic 'C'., is there any other way to do so...

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What a mistake! BSTR type is a generic type for COM. Since COM is applicable for basic 'C' (is it a surprise for you?), so the BSTR type does.

And what about Borland C++? Do you think it's kinda extraterrestrial in Windows world? Or C++ world? :)