LPWSTR與LPSTR轉換，使用USES_CONVERSION

#include 
//在一個函數的循環體中使用A2W等字符轉換宏可能引起棧溢出（內存未釋放）
//參見對應宏的定義
//Ascii -> wchar
USES_CONVERSION
DoSomething(A2W(aStr));

//wchar -> Ascii
USES_CONVERSION
DoSomething(W2A(aStr));

A2W:

//atlconv.h
#define A2W(lpa) (\
   ((_lpa = lpa) == NULL) ? NULL : (\
      _convert = (lstrlenA(_lpa)+1),\
      ATLA2WHELPER((LPWSTR) alloca(_convert*2), _lpa, _convert)))
#define ATLA2WHELPER AtlA2WHelper
inline LPWSTR WINAPI AtlA2WHelper(LPWSTR lpw, LPCSTR lpa, int nChars, UINT acp)
{
   ATLASSERT(lpa != NULL);
   ATLASSERT(lpw != 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] = '\0';
   MultiByteToWideChar(acp, 0, lpa, -1, lpw, nChars);
   return lpw;
}

W2A:

//atlconv.h
#define W2A(lpw) (\
	((_lpw = lpw) == NULL) ? NULL : (\
		(_convert = (ATL::lstrlenW(_lpw)+1), \
		(_convert>INT_MAX/2) ? NULL : \
		ATLW2AHELPER((LPSTR) alloca(_convert*sizeof(WCHAR)), _lpw, _convert*sizeof(WCHAR), _acp))))