谨慎使用A2W等字符转换宏

在一个函数的循环体中使用A2W等字符转换宏可能引起栈溢出。#include <atlconv.h>void fn(){    while(true)    {        {            USES_CONVERSION;            DoSomething(A2W("SomeString"));        }    }}让我们来分析以上的转换宏#define A2W(lpa) (\   ((_lpa = lpa) == NULL) ? NULL : (\      _convert = (lstrlenA(_lpa)+1),\      ATLA2WHELPER((LPWSTR) alloca(_convert*2), _lpa, _convert)))#define ATLA2WHELPER AtlA2WHelperinline 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;}关键的地方在 alloca  内存分配内存上。#define alloca  _alloca_allocaAllocates memory on the stack.Remarks_alloca allocates size bytes from the program stack. The allocated space is automatically freed when the calling functionexits. Therefore, do not pass the pointer value returned by _alloca as an argument to free.问题就在这里，分配的内存是在函数的栈中分配的。而VC编译器默认的栈内存空间是2M。当在一个函数中循环调用它时就会不断的分配栈中的内存。以上问题的解决办法：1、自己写字符转换函数，不要偷懒Function that safely converts a 'WCHAR' String to 'LPSTR':char* ConvertLPWSTRToLPSTR (LPWSTR lpwszStrIn){  LPSTR pszOut = NULL;  if (lpwszStrIn != NULL)  { int nInputStrLen = wcslen (lpwszStrIn); // Double NULL Termination int nOutputStrLen = WideCharToMultiByte (CP_ACP, 0, lpwszStrIn, nInputStrLen, NULL, 0, 0, 0) + 2; pszOut = new char [nOutputStrLen]; if (pszOut) {   memset (pszOut, 0x00, nOutputStrLen);   WideCharToMultiByte(CP_ACP, 0, lpwszStrIn, nInputStrLen, pszOut, nOutputStrLen, 0, 0); }  }  return pszOut;}等等一个一个的实现。2、把字符转换部分放到一个函数中处理。void fn2(){    USES_CONVERSION;    DoSomething(A2W("SomeString"));}void fn(){    while(true)    {        fn2();    }}