[C++] string to wstring

Here is an example for string to wstring transform.

HRESULT DSU_StrToWcs( string strSrc, wstring* wstrDst, UINT nCodepage = CP_UTF8) ;

HRESULT DSU_StrToWcs(string strSrc, wstring* wstrDst, UINT nCodepage)
{
 if ( wstrDst == NULL ) 
  return E_POINTER;

 int iStrLen = strSrc.length() ;

 int nCount = MultiByteToWideChar(nCodepage, 0, strSrc.c_str(), iStrLen, NULL, 0) ;
 WCHAR* pWCHAR = (WCHAR*)alloca(sizeof(WCHAR) * (nCount + 1)) ;

 nCount = MultiByteToWideChar(nCodepage, 0, strSrc.c_str(), iStrLen, pWCHAR, nCount+1) ;
 pWCHAR[nCount] = NULL ;

 *wstrDst = pWCHAR ;

 return S_OK ;
}