std::string to BSTR conversion

[manin21]

Hi everybody,
I have a problem, i'm developing a dll in VC++ 6.0, this dll is for a Vb 6.0 app. that looks somenthing like this:

BSTR __stdcall login (BSTR user,BSTR password){
...
...
std::string validuser = functhatreturnstdstring(user,password);
return ((BSTR)validuser);
}

How can I convert/cast the std::string to BSTR??? or how can I manage the returned std::string in Vb?? I try returnin a char*, const char*, but, when i run the Vb app. it fails, and says: the instruction at memory 0x98797 referencing to memory 0x0980808 could not be read, whats wrong??? I also try returning others data types int, short, float and works fine, also returning this strange datatype BSTR that is like a char * works fine, whats wrong with char *??

in my Vb code I have something like this:

Private Declare Function login Lib "C:\juan\telcel\KlientC++\KlientCpp\Debug\KlientCpp.dll" (ByVal x As String, ByVal y As String) As String
Private Sub Command1_Click()
Text3.Text = Str(login(Text1.Text, Text2.Text))
End Sub

please Help me!!

What I need to do in Vb or Vc++ to this thing work???

[f1shrman]

VB is expecting a BSTR data type to be returned from your dll.

If you do not have to convert the incoming BSTR to std::string then don't and just return the BSTR value.

If you have to convert to a std::string then you need to convert it back into a BSTR before you send it back to VB.

HTH

[xzhang84211]

try this:

BSTR bstrtmp; CString strTmp("hello");
bstrtmp = m_strTmp.AllocSysString();

[Ejaz]

Take a look at How to convert std::string* to BSTR*

[suchuhui80]

	BSTR bstrRet;
	LPWSTR szUnicode;
	if (AscToUnicode (strRet.c_str (),&szUnicode))
	{
		bstrRet=::SysAllocString (szUnicode);



bool AscToUnicode (const char* szAsc,LPWSTR* ppUnicode)
{
		int nWidthCharLen;
		nWidthCharLen=::MultiByteToWideChar(CP_ACP,0,szAsc,::lstrlen (szAsc),NULL,0);
		*ppUnicode=new wchar_t[nWidthCharLen];
		::ZeroMemory (*ppUnicode,nWidthCharLen * 2);
		//dwLen=(DWORD)(nWidthCharLen * sizeof(WCHAR));
		//lpBuffer=new BYTE[dwLen];
		if (::MultiByteToWideChar(CP_ACP,0,szAsc,lstrlen(szAsc),*ppUnicode,nWidthCharLen)==0)
		{			
			delete *ppUnicode;
			*ppUnicode=NULL;
			return false;            
		}
		else		
			return true;
}

there is other way to transfer a string from VC Dll to VB .

VC SIDE
struct MyStru
{
char szMy[1024 * 8];
};

void MyFunc(MyStru* pStru)
{
lstrcpy (pStru->szMy,"fkjsfkjdfj");
}


VB SIDE
type MyStru
{
 Dim szMy as String* (1024* 8).
}
public declare Function MyFunc(byRef  MyStru) ;
// I am not quite sure whether the vb code is correct or not .

but I recommend you to use ActiveX -control instead of DLL,it works perfectly.