#keywords BSTR,C++,CString,MFC
[[TableOfContents]]
=== 'CString' to 'BSTR': ===

Use the AllocSysString member function of the CString:

Code:
{{{#!gcode
CString str("Hello");
BSTR bstr = str.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.

Code:
{{{#!gcode
::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:

Code:
{{{#!gcode
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:
Code:
{{{#!gcode
BSTR bstr;
SomeOLEFunction(bstr);
_bstr_t tmp(bstr, FALSE);   //wrap the BSTR
CString str(static_cast<const char*>(tmp));  //convert it
AfxMessageBox(str, 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.

=== MFC가 아닌 경우. ===
#include <comutil.h>
#pragma comment (lib,"comsuppw.lib" )

=== 기타 ===
What is this BSTR thing, and how does it differ from WCHAR* ? Here is Eric's Complete Guide To BSTR Semantics.
http://blogs.msdn.com/b/ericlippert/archive/2003/09/12/52976.aspx