C / C++ / MFC

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

6-Jan-08 1:59

Hi together,

i'm trying to pass Strings from a vb project to a c++ Dll and from the Dll back to vb in one function.
It will work from VB to the Dll but not back ?!?!?!?!
I'm trying this now for some days and i couldn't find a solution !
You are my last hope !

Here are the codes:
VB:

<br />
Option Explicit<br />
<br />
Private Declare Function fnWin32DLL02 Lib "E:\WORKING\OMRON\GDT\EigeneDLL\C++ DLL mit VB (Test01)\Win32DLL02.dll" (ByVal testParam As String) As String<br />
<br />
Private Sub Form_Load()<br />
    <br />
    Dim x As String<br />
    x = Space$(5)<br />
    Dim test As String<br />
    test = Space$(20)<br />
    <br />
    test = "Übergabe aus VB"<br />
    x = fnWin32DLL02(test)<br />
    MsgBox "X ist: " & x<br />
<br />
End Sub<br />

Dll cpp:

<br />
WIN32DLL02_API BSTR fnWin32DLL02(BSTR s)<br />
{<br />
		BSTR x;<br />
<br />
		x = SysAllocString((BSTR)"abcde");<br />
	 	MessageBox(NULL,(LPCSTR)s,"Info",MB_OK);<br />
<br />
		SysFreeString(s);<br />
		SysFreeString(x);<br />
<br />
		return x;<br />
}<br />

Dll.h

<br />
WIN32DLL02_API BSTR fnWin32DLL02(BSTR);<br />

I hope it is not too much code but it is the best way to show you my problem.

Many, many thanx
hopefully
Croc

CPallini6-Jan-08 2:59

CPallini

6-Jan-08 2:59

CrocodileBuck wrote:
SysFreeString(x);

Why are freeing the (allocated) string you need to return?

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

CrocodileBuck6-Jan-08 3:06

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

6-Jan-08 3:06

Thx Pallini,

for your quick answer i no freeing now Wink | ;)

Bit it still won't work !

Thx again
Croc

CPallini6-Jan-08 3:21

CPallini

6-Jan-08 3:21

Well I think you have to change

CrocodileBuck wrote:
x = SysAllocString((BSTR)"abcde");

with

x = SysAllocString(L"abcde");

but I cannot be sure because I've not a VB6 available at the moment.

BTW what is returned to VB6?

Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

CrocodileBuck6-Jan-08 3:26

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

6-Jan-08 3:26

Thx again Pallini,

i've changed it but it still win't work, is some thing wrong with the vb Code ?
Here is the changed Dll.Cpp:

<br />
WIN32DLL02_API BSTR fnWin32DLL02(LPCSTR s)<br />
{<br />
		BSTR x;<br />
<br />
		x = SysAllocString(L"abcde");<br />
<br />
	 	MessageBox(NULL,s,"Info",MB_OK);<br />
<br />
<br />
		return x;<br />
}<br />

Many thx
Croc

CPallini6-Jan-08 4:01

CPallini

6-Jan-08 4:01

From documentation seems that you have to pass back an ANSI string, which will be translated by VB6, i.e. try to change

CrocodileBuck wrote:

x = SysAllocString(L"abcde");

char * psz = "abcde";
x = SysAllocStringLen(psz, strlen(psz));

Again, I haven't VB6 at hand,so the attempt is up to you (I apologize for Rose | [Rose]

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

Nemanja Trifunovic6-Jan-08 6:09

Nemanja Trifunovic

6-Jan-08 6:09

You can use BSTR only if you have a COM dll, which you obviously don't. So, try returning good ol char* instead.

Programming Blog

utf8-cpp

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

Rajesh R Subramanian6-Jan-08 6:18

Rajesh R Subramanian

6-Jan-08 6:18

Nemanja Trifunovic wrote:
You can use BSTR only if you have a COM dll, which you obviously don't. So, try returning good ol char* instead.

Are you sure? If I remember it right, I've returned BSTR from a regular dll for some reason and I think it worked. I am not on my Dev machine now to verify it.

Nobody can give you wiser advice than yourself. - Cicero
.·´¯`·->Rajesh<-·´¯`·.
Codeproject.com: Visual C++ MVP

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

Nemanja Trifunovic6-Jan-08 6:30

Nemanja Trifunovic

6-Jan-08 6:30

Rajesh R Subramanian wrote:
I've returned BSTR from a regular dll for some reason and I think it worked.

IIRC, it is "doable" if you catch it as a byte array on the VB side, but it does not work out of the box.

Programming Blog

utf8-cpp

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

Michael Dunn6-Jan-08 7:30

Michael Dunn

6-Jan-08 7:30

In addition to what the other posts said, you are also misusing casts.
(BSTR)"abcde" is wrong - a string literal is not a BSTR.
(LPCSTR)s is wrong - a BSTR is not a const char*.

Casts are not the right way to solve compiler errors. Check out The Complete Guide to C++ Strings, Part I - Win32 Character Encodings[^] so you get an understaning of string encodings.

--Mike--
Visual C++ MVP Cool | :cool:

LINKS~! CP SearchBar v3.0 | C++ Forum FAQ

Dunder-Mifflin, this is Pam.

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

Maxwell Chen6-Jan-08 7:46

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

6-Jan-08 7:46

BSTR[^]

typedef WCHAR  OLECHAR;
typedef OLECHAR FAR * BSTR;

WCHAR[^]

#if !defined(_NATIVE_WCHAR_T_DEFINED)
  typedef unsigned short WCHAR;
#else
  typedef wchar_t WCHAR;
#endif

Maxwell Chen

CrocodileBuck7-Jan-08 0:46

Re: Strings from a c++ Dll to VB 6.0 and vice versa !

7-Jan-08 0:46

Firs of all,
*THX* to all of you for your answers,
i tried it all ways but it still wont work, i could not find the mistake, i really don't know what i coud do !

These are my latest Codes:
VB:

<br />
Option Explicit<br />
<br />
Private Declare Function fnWin32DLL02 Lib "E:\WORKING\OMRON\GDT\EigeneDLL\Übergabe eines Strings aus C++ Dll\Win32DLL02.dll" () As String<br />
<br />
Private Sub Form_Load()<br />
    <br />
    Dim x As String<br />
    <br />
    x = Space$(3)<br />
    x = fnWin32DLL02()<br />
    MsgBox "X ist: " & x<br />
    <br />
End Sub<br />

Cpp:

<br />
WIN32DLL02_API LPCSTR fnWin32DLL02(void)<br />
{<br />
		LPCSTR s;<br />
		s = "abc";<br />
	//  s = SysAllocString(L"abc");<br />
	  // 	SysFreeString(s);<br />
		return s;<br />
}<br />

Many thanx again
Croc

Mike Dimmick6-Jan-08 7:53

Mike Dimmick

6-Jan-08 7:53

When using a Declare statement, Visual Basic converts strings (which it stores internally as Unicode UTF-16) to ANSI, using the default code page. There is no way to control which code page is used.

Your C++ DLL should therefore be ANSI throughout, i.e. using char* and derived types (e.g. LPSTR, LPCSTR).

On return from the function, ByRef parameters are converted back to Unicode as appropriate.

DoEvents: Generating unexpected recursion since 1991

Device driver

messages5-Jan-08 23:20

messages

5-Jan-08 23:20

Hi everyone
Can you give give me a good tutorial about make device driver of course maybe you will be say that codeproject has articles about make it or if you use of google you can find a lot info about it but I want to start of first,what is device driver and then start to writing code?
Thanks

Maxwell Chen5-Jan-08 23:39

5-Jan-08 23:39

1) You have to install WDK (Windows Driver Kit) to compile the source code. Visual Studio (Visual C++) is not able to make device drivers (unless you install some third-party add-on to Visual C++).

2) Different type of device drivers require different callback functions. For example, a card reader driver has different callbacks from what a SCSI miniport driver has.

Maxwell Chen

messages5-Jan-08 23:56

messages

5-Jan-08 23:56

Can you give me abour device driver what is it and I have VS2005 does it perfect for make it?
Thanks

Maxwell Chen6-Jan-08 0:04

6-Jan-08 0:04

messages wrote:
abour device driver what is it

A device driver is to control a hardware device.

messages wrote:
I have VS2005 does it perfect for make it?

No, VS2005 is useless to make a device driver. (But is good to view source code.)
You have to get a copy of WDK and install it. It will brought you some shortcuts to open DOS-box command-line environments for you to compile the source code.

Windows Driver Kit Homepage[^]

Maxwell Chen

How can i find some old articles?

messages6-Jan-08 0:30

messages

6-Jan-08 0:30

Thanks

lichongbin5-Jan-08 23:16

lichongbin

5-Jan-08 23:16

Last year I can find some articles which is written for beginners. After upgrade those articles are missing. Who can tell me how to find them?

There is a will,there is a way!

Re: How can i find some old articles?

Hamid_RT5-Jan-08 23:46

Hamid_RT

5-Jan-08 23:46

What article or articles you need to see?

Re: How can i find some old articles?

lichongbin6-Jan-08 14:17

lichongbin

6-Jan-08 14:17

I downloaded a sample program in codeproject.com last year. I can’t find the article along with it.The demo project is named “TreePropSheetDemo”. Can you help me find it or tell me how to find it?

There is a will,there is a way!

Re: How can i find some old articles?

Maxwell Chen6-Jan-08 16:26