MFC String: How to convert between a 'CString' and a 'BSTR'?

[Gabriel Fleseriu]

Q: How to convert between a 'CString' and a 'BSTR'?

A:

'CString' to 'BSTR':

Use the AllocSysString member function of the CString:

CString cs("Hello");
BSTR bstr = cs.AllocSysString();

If you pass the 'BSTR' to some OLE function, this will normally free the 'BSTR' memory when done with it.

If you use the 'BSTR' by yourself, dont forget to call '::SysFreeString()' when you're done with it.

::SysFreeString(bstr);

'BSTR' to 'CString':

You will mostly need this when you have some OLE function that returns a 'BSTR'. Such an OLE Function will basically do something like this:

HRESULT SomeOLEFunction(BSTR& bstr)
{
  bstr = ::SysAllocString(L"Hello");
  return S_OK;
}

Use a temporary variable of the type '_bstr_t' to wrap the 'BSTR'. This way you handle both the 208 and make sure that you have no memory leak:

BSTR bstr;
SomeOLEFunction(bstr);
_bstr_t tmp(bstr, FALSE);   //wrap the BSTR
CString cs(static_cast<const char*>(tmp));  //convert it
AfxMessageBox(cs, MB_OK, 0);
// when tmp goes out of scope it will free the BSTRs memory

Note, that this won't work in a UNICODE build.