How to convert _bstr_t to CString

Question

I have a _bstr_t variable bstrErr and I am having a CString variable csError. How do I set the value which come in

Answer 1

If you compile for Unicode - just assign the encapsulated BSTR to the CString. If you compile for ANSI you'll have to use WideCharToMultiByte() for conversion.

Also beware that the encapsulated BSTR can be null which corresponds to an empty string. If you don't take care of this your program will run into undefined behaviour.

Answer 2

CStringT,CString, CStringA, and CStringW:

• CStringT is a complicated class template based on an arbitrary character type and helper class templates for managing the storage and the features.
• The class CString is a typedef of the template class that uses the TCHAR character type. TCHARis a generic type that resolves to wchar if the macro UNICODE is set, else to char.
• The class CStringA is a typedef of the template class that uses internally the narrow character type char.
• The class CStringW is a typedef of the template class that uses internally the wide character type wchar_t.

I never use CString in code, instead I always use the explicit classes CStringA or CStringW. The classes CString* have constructors that accept narrow and wide strings. The same is true for _bstr_t. Strings of type BSTR must be allocated by the function SysAllocString() that expects an OLECHAR string, hence in Win32/64 a wide string. If you want to copy a _bstr_t that contains Unicode to a CStringA you must convert it to UTF8. I use the classes CW2A and CA2W for conversion.

In the following event function of a Word add-in, I show the use of these types:

STDMETHODIMP CConnect::TestButtonClicked(IDispatch* Command)
{
  BSTR smi = SysAllocString(L"Two smileys                                                                     

                                                        
            

Answer 3

Is it not possible just to cast it:

_bstr_t b("Steve");
CString cs;
cs = (LPCTSTR) b;

I think this should work when the project is Unicode.

Answer 4

CString has contructors and assignment operators for both LPCSTR and LPCWSTR, so there is never a need to call WideCharToMultiByte, and you can't get the casting wrong in unicode or non-unicode mode.

You can just assign the string this way:

csError = bstrErr.GetBSTR();

Or use the constructor CString csError( bstrErr.GetBSTR() );

I'm using GetBSTR. It's the same thing as casting bstrErr with (LPCWSTR), but I prefer it for legibility.

Answer 5

BSTR myBSTRVal;
CString BSTRasCString("")
char  szValue[MAX_PATH] = "";

// This will map the BSTR to a new character string (szValue)
WideCharToMultiByte(CP_ACP, 0, myBSTRVal, -1, szValue, sizeof(szValue), NULL, 
NULL);
BSTRasCString.Format("%s", szValue);                
BSTRasCString.TrimLeft();
BSTRasCString.TrimRight();