Howto return a String from c++ to vb

[Chris_CJM]

Hi,

I've tryed to return a string from my own made dll to visual basic but i'm unsuccesful doing this.

Does anybody know how to do this?

This is my code(this does'nt work!)

void DBSOCK_API test(LPSTR returnStr){

char buffer[]="1234 testing";
strcpy(returnStr,buffer);
}


and in visual basic:

Declare Sub test Lib "dbSock" (ByVal st As String)


Private Sub Command1_Click()
Dim myString
test (myString)
MsgBox myString
End Sub


The message box displayed nothing

Does anybody know what I'm doing wrong

note that I'm using Microsoft eMbedded Visual Tools.

[Chris_CJM]

Anybody alive here?
maybe i'll try to order some pizza. That always helps

[Zaei]

I dont actually know the answer, but I can give you some info to perhaps help you out.

VB strings are Unicode, which means that each character uses two bytes. The C++ equivalent is a BSTR.

You can typecast to to an LPSTR from a BSTR to get standard 1 byte characters.

Z.

[parksie]

Actually, BSTR is nominally for OLE. For normal C++, you want LPWSTR, or in real terms, wchar_t* (as opposed to char*).

www.parksie.uklinux.net/StringDLL.zip (I think it's still there).

VB will pass an ANSI string to a DLL (or a pointer to one if you're filling it from the DLL), unless you specifically convert it to Unicode using StrConv(..., vbUnicode, ...).

[Zaei]

::is enlightened:: Thanks parksie (again =).

Z.

[Chris_CJM]

Some good advice, thank you


I've got some something working. If you send a pointer to an array of unsigned shorts it works. This function does the trick:

<code>

void charToShort (unsigned short *outStr,char *inStr,int strLen)
{
int counter = 0;
for(counter=0;counter < strLen;counter++)
{
outStr[counter] = inStr[counter];
}
//terminate the string with a 0
outStr[counter]=0;
}


unsigned short DBSOCK_API *test (void){

unsigned short tmpBuffer[255];

charToShort(tmpBuffer,"1234",4);
return tmpBuffer;
}
</code>

[parksie]

If you want to convert char* to wchar_t*, then use the MultiByteToWideChar function from the Windows API, or wcsmbcs (it's something like that, I can't remember) from the C standard library.

Don't just try and convert the number values.