A2W no ATL

#define USES_CONVERSION int _convert = 0; (_convert); UINT _acp = CP_THREAD_ACP; (_acp); LPCWSTR _lpw = NULL; (_lpw); LPCSTR _lpa = NULL; (_lpa)

inline __out_ecount_z_opt(nChars) LPWSTR WINAPI AtlA2WHelper(__out_ecount_z(nChars) LPWSTR lpw, __in_z LPCSTR lpa, __in int nChars, __in UINT acp) throw()
{
	assert(lpa != NULL);
	assert(lpw != NULL);
	if (lpw == NULL || lpa == NULL)
		return NULL;
	// verify that no illegal character present
	// since lpw was allocated based on the size of lpa
	// don't worry about the number of chars
	lpw[0] = '';
	int ret = MultiByteToWideChar(acp, 0, lpa, -1, lpw, nChars);
	if(ret == 0)
	{
		assert(FALSE);
		return NULL;
	}		
	return lpw;
}

#define A2W(lpa) (
	((_lpa = lpa) == NULL) ? NULL : (
		_convert = (lstrlenA(_lpa)+1),
		(INT_MAX/2<_convert)? NULL :  
		AtlA2WHelper((LPWSTR) alloca(_convert*sizeof(WCHAR)), _lpa, _convert, _acp)))