Using CString in _T value - c++

Question

I am making use of the EAGetMail Library but instead of hard coding the username and password, I am trying to pass two CString values as the credentials but it doesn't seem to like that.
CString username;
pObject->GetDlgItemText(IDC_EDIT1, username);
CString password;
pObject->GetDlgItemText(IDC_EDIT2, password);
IMailServerPtr oServer = NULL;
oServer.CreateInstance(__uuidof(EAGetMailObjLib::MailServer));
oServer->User = _T("myusername"); //THIS WORKS HARD CODED
Doesn't work:
oServer->User = username //Error, cannot be called with given argument list
I also tried:
oServer->User = _T(username); //L Username is undefined.
I guess I need to convert the CString somehow?
Tried the following:
//Get Email Credentials
CString username;
pObject->GetDlgItemText(IDC_EDIT1, username);
CString password;
pObject->GetDlgItemText(IDC_EDIT2, password);
_bstr_t usernamea(pObject->GetDlgItemText(IDC_EDIT1, username));
_bstr_t passworda(pObject->GetDlgItemText(IDC_EDIT2, password));

Answer 1

This worked.
//Get Email Credentials
CString username;
pObject->GetDlgItemText(IDC_EDIT1, username);
CString password;
pObject->GetDlgItemText(IDC_EDIT2, password);
CComBSTR bstrUsername; bstrUsername = username.AllocSysString();
_bstr_t usernamea(bstrUsername);
CComBSTR bstrPassword; bstrPassword = password.AllocSysString();
_bstr_t passworda(bstrPassword);
oServer->User = usernamea;
oServer->Password = passworda;

Answer 2

Using C-style character pointers is the price we have to pay for making lower-level system calls to the OS. Microsoft makes it more complicated because it has pairs of system calls, one for char * and wchar_t for the other. Typically you want to be consistent with one set or the other, so Microsoft provides a host of macros so that you can refer to the typical type of character TCHAR in the abstract.
_T is a Microsoft-specific macro that you should use only on string literals. It prepends an L to the literal when compiling a Unicode program (when TCHAR IS wchar_t) and does nothing for other programs (where TCHAR is char).
You've demonstrated that IMailServer::User will accept a string literal of type TCHAR const * but you store your data in a n MFC CString.
From the documentation of the MFC CString object:
A CString object keeps character data in a CStringData object. CString accepts NULL-terminated C-style strings. CString tracks the string length for faster performance, but it also retains the NULL character in the stored character data to support conversion to LPCWSTR. CString includes the null terminator when it exports a C-style string.
You can convert a CString to a TCHAR * but for this you have to do it explicitly:
oServer->User = (LPCTSTR)username;
or the C++ way
oServer->User = static_cast<TCHAR const *>(username);
this will call CStringT<TCHAR>::operator PCXSTR to get the raw character pointer.
(Personally I'd use a std::basic_string<TCHAR> rather than a CString but that's just me).