date：2018.10.23
USES_CONVERSION是ATL中的一个宏定义。用于编码转换(用的比较多的是CString向LPCWSTR转换)。在ATL下使用要包含头文件#include "atlconv.h"
使用USES_CONVERSION一定要小心，它们从堆栈上分配内存，直到调用它的函数返回，该内存不会被释放。如果在一个循环中，这个宏被反复调用几万次，将不可避免的产生stackoverflow。
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：
A2W
#ifdef _CONVERSION_USES_THREAD_LOCALE
#define A2W(lpa) (\
((_lpa = lpa) == NULL) ? NULL : (\
_convert = (lstrlenA(_lpa)+1),\
ATLA2WHELPER((LPWSTR) alloca(_convert*2), _lpa, _convert, _acp)))
#else
#define A2W(lpa) (\
((_lpa = lpa) == NULL) ? NULL : (\
_convert = (lstrlenA(_lpa)+1),\
ATLA2WHELPER((LPWSTR) alloca(_convert*2), _lpa, _convert)))
#endif
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;
}
关键的地方在 alloca 内存分配内存上。
#define alloca _alloca
_alloca
Allocates memory on the stack.
Remarks
_alloca allocates size bytes from the program stack. The allocated space is automatically freed when the calling function
exits. 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();
}
}
如果不知道这点问题，在使用后崩溃时很难查出崩溃原因的。
注：
在需要进行编码转换的函数开头，写上USES_CONVERSION；
使用USES_CONVERSION宏需要声明头文件
atlconv.h代码如下：
// This is a part of the Active Template Library.
// Copyright (C) 1996-1998 Microsoft Corporation
// All rights reserved.
//
// This source code is only intended as a supplement to the
// Active Template Library Reference and related
// electronic documentation provided with the library.
// See these sources for detailed information regarding the
// Active Template Library product.
#ifndef __ATLCONV_H__
#define __ATLCONV_H__
#ifndef __cplusplus
#error ATL requires C++ compilation (use a .cpp suffix)
#endif
#include
#ifndef _INC_MALLOC
#include
#endif // _INC_MALLOC
#pragma pack(push,8)
#ifdef _CONVERSION_USES_THREAD_LOCALE
#ifndef _DEBUG
#define USES_CONVERSION int _convert; _convert; UINT _acp = GetACP(); _acp; LPCWSTR _lpw; _lpw; LPCSTR _lpa; _lpa
#else
#define USES_CONVERSION int _convert = 0; _convert; UINT _acp = GetACP(); _acp; LPCWSTR _lpw = NULL; _lpw; LPCSTR _lpa = NULL; _lpa
#endif
#else
#ifndef _DEBUG
#define USES_CONVERSION int _convert; _convert; UINT _acp = CP_ACP; _acp; LPCWSTR _lpw; _lpw; LPCSTR _lpa; _lpa
#else
#define USES_CONVERSION int _convert = 0; _convert; UINT _acp = CP_ACP; _acp; LPCWSTR _lpw = NULL; _lpw; LPCSTR _lpa = NULL; _lpa
#endif
#endif
#ifdef _WINGDI_
ATLAPI_(LPDEVMODEA) AtlDevModeW2A(LPDEVMODEA lpDevModeA, LPDEVMODEW lpDevModeW);
#endif
/////////////////////////////////////////////////////////////////////////////
// Global UNICODEANSI translation helpers
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;
}
inline LPSTR WINAPI AtlW2AHelper(LPSTR lpa, LPCWSTR lpw, int nChars, UINT acp)
{
ATLASSERT(lpw != NULL);
ATLASSERT(lpa != NULL);
// verify that no illegal character present
// since lpa was allocated based on the size of lpw
// don't worry about the number of chars
lpa[0] = '\0';
WideCharToMultiByte(acp, 0, lpw, -1, lpa, nChars, NULL, NULL);
return lpa;
}
inline LPWSTR WINAPI AtlA2WHelper(LPWSTR lpw, LPCSTR lpa, int nChars)
{
return AtlA2WHelper(lpw, lpa, nChars, CP_ACP);
}
inline LPSTR WINAPI AtlW2AHelper(LPSTR lpa, LPCWSTR lpw, int nChars)
{
return AtlW2AHelper(lpa, lpw, nChars, CP_ACP);
}
#ifdef _CONVERSION_USES_THREAD_LOCALE
#ifdef ATLA2WHELPER
#undef ATLA2WHELPER
#undef ATLW2AHELPER
#endif
#define ATLA2WHELPER AtlA2WHelper
#define ATLW2AHELPER AtlW2AHelper
#else
#ifndef ATLA2WHELPER
#define ATLA2WHELPER AtlA2WHelper
#define ATLW2AHELPER AtlW2AHelper
#endif
#endif
#ifdef _CONVERSION_USES_THREAD_LOCALE
#define A2W(lpa) (\
((_lpa = lpa) == NULL) ? NULL : (\
_convert = (lstrlenA(_lpa)+1),\
ATLA2WHELPER((LPWSTR) alloca(_convert*2), _lpa, _convert, _acp)))
#else
#define A2W(lpa) (\
((_lpa = lpa) == NULL) ? NULL : (\
_convert = (lstrlenA(_lpa)+1),\
ATLA2WHELPER((LPWSTR) alloca(_convert*2), _lpa, _convert)))
#endif
#ifdef _CONVERSION_USES_THREAD_LOCALE
#define W2A(lpw) (\
((_lpw = lpw) == NULL) ? NULL : (\
_convert = (lstrlenW(_lpw)+1)*2,\
ATLW2AHELPER((LPSTR) alloca(_convert), _lpw, _convert, _acp)))
#else
#define W2A(lpw) (\
((_lpw = lpw) == NULL) ? NULL : (\
_convert = (lstrlenW(_lpw)+1)*2,\
ATLW2AHELPER((LPSTR) alloca(_convert), _lpw, _convert)))
#endif
#define A2CW(lpa) ((LPCWSTR)A2W(lpa))
#define W2CA(lpw) ((LPCSTR)W2A(lpw))
#if defined(_UNICODE)
// in these cases the default (TCHAR) is the same as OLECHAR
inline size_t ocslen(LPCOLESTR x) { return lstrlenW(x); }
inline OLECHAR* ocscpy(LPOLESTR dest, LPCOLESTR src) { return lstrcpyW(dest, src); }
inline OLECHAR* ocscat(LPOLESTR dest, LPCOLESTR src) { return lstrcatW(dest, src); }
inline LPCOLESTR T2COLE(LPCTSTR lp) { return lp; }
inline LPCTSTR OLE2CT(LPCOLESTR lp) { return lp; }
inline LPOLESTR T2OLE(LPTSTR lp) { return lp; }
inline LPTSTR OLE2T(LPOLESTR lp) { return lp; }
inline LPOLESTR CharNextO(LPCOLESTR lp) {return CharNextW(lp);}
#elif defined(OLE2ANSI)
// in these cases the default (TCHAR) is the same as OLECHAR
inline size_t ocslen(LPCOLESTR x) { return lstrlen(x); }
inline OLECHAR* ocscpy(LPOLESTR dest, LPCOLESTR src) { return lstrcpy(dest, src); }
inline OLECHAR* ocscat(LPOLESTR dest, LPCOLESTR src) { return ocscpy(dest+ocslen(dest), src); }
inline LPCOLESTR T2COLE(LPCTSTR lp) { return lp; }
inline LPCTSTR OLE2CT(LPCOLESTR lp) { return lp; }
inline LPOLESTR T2OLE(LPTSTR lp) { return lp; }
inline LPTSTR OLE2T(LPOLESTR lp) { return lp; }
inline LPOLESTR CharNextO(LPCOLESTR lp) {return CharNext(lp);}
#else
inline size_t ocslen(LPCOLESTR x) { return lstrlenW(x); }
//lstrcpyW doesn't work on Win95, so we do this
inline OLECHAR* ocscpy(LPOLESTR dest, LPCOLESTR src)
{return (LPOLESTR) memcpy(dest, src, (lstrlenW(src)+1)*sizeof(WCHAR));}
inline OLECHAR* ocscat(LPOLESTR dest, LPCOLESTR src) { return ocscpy(dest+ocslen(dest), src); }
//CharNextW doesn't work on Win95 so we use this
#define T2COLE(lpa) A2CW(lpa)
#define T2OLE(lpa) A2W(lpa)
#define OLE2CT(lpo) W2CA(lpo)
#define OLE2T(lpo) W2A(lpo)
inline LPOLESTR CharNextO(LPCOLESTR lp) {return (LPOLESTR) ((*lp) ? (lp+1) : lp);}
#endif
#ifdef OLE2ANSI
inline LPOLESTR A2OLE(LPSTR lp) { return lp;}
inline LPSTR OLE2A(LPOLESTR lp) { return lp;}
#define W2OLE W2A
#define OLE2W A2W
inline LPCOLESTR A2COLE(LPCSTR lp) { return lp;}
inline LPCSTR OLE2CA(LPCOLESTR lp) { return lp;}
#define W2COLE W2CA
#define OLE2CW A2CW
#else
inline LPOLESTR W2OLE(LPWSTR lp) { return lp; }
inline LPWSTR OLE2W(LPOLESTR lp) { return lp; }
#define A2OLE A2W
#define OLE2A W2A
inline LPCOLESTR W2COLE(LPCWSTR lp) { return lp; }
inline LPCWSTR OLE2CW(LPCOLESTR lp) { return lp; }
#define A2COLE A2CW
#define OLE2CA W2CA
#endif
#ifdef _UNICODE
#define T2A W2A
#define A2T A2W
inline LPWSTR T2W(LPTSTR lp) { return lp; }
inline LPTSTR W2T(LPWSTR lp) { return lp; }
#define T2CA W2CA
#define A2CT A2CW
inline LPCWSTR T2CW(LPCTSTR lp) { return lp; }
inline LPCTSTR W2CT(LPCWSTR lp) { return lp; }
#else
#define T2W A2W
#define W2T W2A
inline LPSTR T2A(LPTSTR lp) { return lp; }
inline LPTSTR A2T(LPSTR lp) { return lp; }
#define T2CW A2CW
#define W2CT W2CA
inline LPCSTR T2CA(LPCTSTR lp) { return lp; }
inline LPCTSTR A2CT(LPCSTR lp) { return lp; }
#endif
inline BSTR A2WBSTR(LPCSTR lp, int nLen = -1)
{
USES_CONVERSION;
BSTR str = NULL;
int nConvertedLen = MultiByteToWideChar(_acp, 0, lp,
nLen, NULL, NULL)-1;
str = ::SysAllocStringLen(NULL, nConvertedLen);
if (str != NULL)
{
MultiByteToWideChar(_acp, 0, lp, -1,
str, nConvertedLen);
}
return str;
}
inline BSTR OLE2BSTR(LPCOLESTR lp) {return ::SysAllocString(lp);}
#if defined(_UNICODE)
// in these cases the default (TCHAR) is the same as OLECHAR
inline BSTR T2BSTR(LPCTSTR lp) {return ::SysAllocString(lp);}
inline BSTR A2BSTR(LPCSTR lp) {USES_CONVERSION; return A2WBSTR(lp);}
inline BSTR W2BSTR(LPCWSTR lp) {return ::SysAllocString(lp);}
#elif defined(OLE2ANSI)
// in these cases the default (TCHAR) is the same as OLECHAR
inline BSTR T2BSTR(LPCTSTR lp) {return ::SysAllocString(lp);}
inline BSTR A2BSTR(LPCSTR lp) {return ::SysAllocString(lp);}
inline BSTR W2BSTR(LPCWSTR lp) {USES_CONVERSION; return ::SysAllocString(W2COLE(lp));}
#else
inline BSTR T2BSTR(LPCTSTR lp) {USES_CONVERSION; return A2WBSTR(lp);}
inline BSTR A2BSTR(LPCSTR lp) {USES_CONVERSION; return A2WBSTR(lp);}
inline BSTR W2BSTR(LPCWSTR lp) {return ::SysAllocString(lp);}
#endif
#ifdef _WINGDI_
/////////////////////////////////////////////////////////////////////////////
// Global UNICODEANSI translation helpers
inline LPDEVMODEW AtlDevModeA2W(LPDEVMODEW lpDevModeW, LPDEVMODEA lpDevModeA)
{
USES_CONVERSION;
if (lpDevModeA == NULL)
return NULL;
ATLASSERT(lpDevModeW != NULL);
AtlA2WHelper(lpDevModeW->dmDeviceName, (LPCSTR)lpDevModeA->dmDeviceName, 32*sizeof(WCHAR), _acp);
memcpy(&lpDevModeW->dmSpecVersion, &lpDevModeA->dmSpecVersion,
offsetof(DEVMODEW, dmFormName) - offsetof(DEVMODEW, dmSpecVersion));
AtlA2WHelper(lpDevModeW->dmFormName, (LPCSTR)lpDevModeA->dmFormName, 32*sizeof(WCHAR), _acp);
memcpy(&lpDevModeW->dmLogPixels, &lpDevModeA->dmLogPixels,
sizeof(DEVMODEW) - offsetof(DEVMODEW, dmLogPixels));
if (lpDevModeA->dmDriverExtra != 0)
memcpy(lpDevModeW+1, lpDevModeA+1, lpDevModeA->dmDriverExtra);
lpDevModeW->dmSize = sizeof(DEVMODEW);
return lpDevModeW;
}
inline LPTEXTMETRICW AtlTextMetricA2W(LPTEXTMETRICW lptmW, LPTEXTMETRICA lptmA)
{
USES_CONVERSION;
if (lptmA == NULL)
return NULL;
ATLASSERT(lptmW != NULL);
memcpy(lptmW, lptmA, sizeof(LONG) * 11);
memcpy(&lptmW->tmItalic, &lptmA->tmItalic, sizeof(BYTE) * 5);
MultiByteToWideChar(_acp, 0, (LPCSTR)&lptmA->tmFirstChar, 1, &lptmW->tmFirstChar, 1);
MultiByteToWideChar(_acp, 0, (LPCSTR)&lptmA->tmLastChar, 1, &lptmW->tmLastChar, 1);
MultiByteToWideChar(_acp, 0, (LPCSTR)&lptmA->tmDefaultChar, 1, &lptmW->tmDefaultChar, 1);
MultiByteToWideChar(_acp, 0, (LPCSTR)&lptmA->tmBreakChar, 1, &lptmW->tmBreakChar, 1);
return lptmW;
}
inline LPTEXTMETRICA AtlTextMetricW2A(LPTEXTMETRICA lptmA, LPTEXTMETRICW lptmW)
{
USES_CONVERSION;
if (lptmW == NULL)
return NULL;
ATLASSERT(lptmA != NULL);
memcpy(lptmA, lptmW, sizeof(LONG) * 11);
memcpy(&lptmA->tmItalic, &lptmW->tmItalic, sizeof(BYTE) * 5);
WideCharToMultiByte(_acp, 0, &lptmW->tmFirstChar, 1, (LPSTR)&lptmA->tmFirstChar, 1, NULL, NULL);
WideCharToMultiByte(_acp, 0, &lptmW->tmLastChar, 1, (LPSTR)&lptmA->tmLastChar, 1, NULL, NULL);
WideCharToMultiByte(_acp, 0, &lptmW->tmDefaultChar, 1, (LPSTR)&lptmA->tmDefaultChar, 1, NULL, NULL);
WideCharToMultiByte(_acp, 0, &lptmW->tmBreakChar, 1, (LPSTR)&lptmA->tmBreakChar, 1, NULL, NULL);
return lptmA;
}
#ifndef ATLDEVMODEA2W
#define ATLDEVMODEA2W AtlDevModeA2W
#define ATLDEVMODEW2A AtlDevModeW2A
#define ATLTEXTMETRICA2W AtlTextMetricA2W
#define ATLTEXTMETRICW2A AtlTextMetricW2A
#endif
#define DEVMODEW2A(lpw)\
((lpw == NULL) ? NULL : ATLDEVMODEW2A((LPDEVMODEA)alloca(sizeof(DEVMODEA)+lpw->dmDriverExtra), lpw))
#define DEVMODEA2W(lpa)\
((lpa == NULL) ? NULL : ATLDEVMODEA2W((LPDEVMODEW)alloca(sizeof(DEVMODEW)+lpa->dmDriverExtra), lpa))
#define TEXTMETRICW2A(lptmw)\
((lptmw == NULL) ? NULL : ATLTEXTMETRICW2A((LPTEXTMETRICA)alloca(sizeof(TEXTMETRICA)), lptmw))
#define TEXTMETRICA2W(lptma)\
((lptma == NULL) ? NULL : ATLTEXTMETRICA2W((LPTEXTMETRICW)alloca(sizeof(TEXTMETRICW)), lptma))
#ifdef OLE2ANSI
#define DEVMODEOLE DEVMODEA
#define LPDEVMODEOLE LPDEVMODEA
#define TEXTMETRICOLE TEXTMETRICA
#define LPTEXTMETRICOLE LPTEXTMETRICA
#else
#define DEVMODEOLE DEVMODEW
#define LPDEVMODEOLE LPDEVMODEW
#define TEXTMETRICOLE TEXTMETRICW
#define LPTEXTMETRICOLE LPTEXTMETRICW
#endif
#if defined(_UNICODE)
// in these cases the default (TCHAR) is the same as OLECHAR
inline LPDEVMODEW DEVMODEOLE2T(LPDEVMODEOLE lp) { return lp; }
inline LPDEVMODEOLE DEVMODET2OLE(LPDEVMODEW lp) { return lp; }
inline LPTEXTMETRICW TEXTMETRICOLE2T(LPTEXTMETRICOLE lp) { return lp; }
inline LPTEXTMETRICOLE TEXTMETRICT2OLE(LPTEXTMETRICW lp) { return lp; }
#elif defined(OLE2ANSI)
// in these cases the default (TCHAR) is the same as OLECHAR
inline LPDEVMODE DEVMODEOLE2T(LPDEVMODEOLE lp) { return lp; }
inline LPDEVMODEOLE DEVMODET2OLE(LPDEVMODE lp) { return lp; }
inline LPTEXTMETRIC TEXTMETRICOLE2T(LPTEXTMETRICOLE lp) { return lp; }
inline LPTEXTMETRICOLE TEXTMETRICT2OLE(LPTEXTMETRIC lp) { return lp; }
#else
#define DEVMODEOLE2T(lpo) DEVMODEW2A(lpo)
#define DEVMODET2OLE(lpa) DEVMODEA2W(lpa)
#define TEXTMETRICOLE2T(lptmw) TEXTMETRICW2A(lptmw)
#define TEXTMETRICT2OLE(lptma) TEXTMETRICA2W(lptma)
#endif
#endif //_WINGDI_
#pragma pack(pop)
#ifndef _ATL_DLL_IMPL
#ifndef _ATL_DLL
#define _ATLCONV_IMPL
#endif
#endif
#endif // __ATLCONV_H__
/////////////////////////////////////////////////////////////////////////////
#ifdef _ATLCONV_IMPL
#ifdef _WINGDI_
ATLINLINE ATLAPI_(LPDEVMODEA) AtlDevModeW2A(LPDEVMODEA lpDevModeA, LPDEVMODEW lpDevModeW)
{
USES_CONVERSION;
if (lpDevModeW == NULL)
return NULL;
ATLASSERT(lpDevModeA != NULL);
AtlW2AHelper((LPSTR)lpDevModeA->dmDeviceName, lpDevModeW->dmDeviceName, 32*sizeof(char), _acp);
memcpy(&lpDevModeA->dmSpecVersion, &lpDevModeW->dmSpecVersion,
offsetof(DEVMODEA, dmFormName) - offsetof(DEVMODEA, dmSpecVersion));
AtlW2AHelper((LPSTR)lpDevModeA->dmFormName, lpDevModeW->dmFormName, 32*sizeof(char), _acp);
memcpy(&lpDevModeA->dmLogPixels, &lpDevModeW->dmLogPixels,
sizeof(DEVMODEA) - offsetof(DEVMODEA, dmLogPixels));
if (lpDevModeW->dmDriverExtra != 0)
memcpy(lpDevModeA+1, lpDevModeW+1, lpDevModeW->dmDriverExtra);
lpDevModeA->dmSize = sizeof(DEVMODEA);
return lpDevModeA;
}
#endif //_WINGDI
//Prevent pulling in second time
#undef _ATLCONV_IMPL
#endif // _ATLCONV_IMPL
