測(cè)試代碼如下：

	char szText[256] = {0xA6,0xA7,0xA8,0xA9};
	/*
	char szText[256] = {0};
	for (int nIndex = 1; nIndex < 256; nIndex++)
	{
		szText[nIndex - 1] = (char)nIndex;
	}
	*/
	CString strText = szText;

	CString strLower = strText;
	strLower.MakeLower();

注意A8被轉(zhuǎn)換了。

char szText[256] = {0xA6,0xA7,0xA8,0xA9};情況
VC6，VC2013，在WIN7系統(tǒng)的情況下

a6 a7 a8 a9 00

 都會(huì)被轉(zhuǎn)換為
 a6 c7 a8 a9 00
結(jié)論：調(diào)用CString的MakeLower(),要確保CString沒(méi)有亂碼的情況。

建議使用STL的string,代碼如下：

char szText[256] = {0xA6,0xA7,0xA8,0xA9};
string strTest = szText;
std::transform(strTest.begin(), strTest.end(), strTest.begin(), ::tolower);

經(jīng)過(guò)IDA跟蹤分析，CString最終調(diào)用MSVCRT(D).dll的_mbslwr(char* string)函數(shù)，

char *__cdecl _mbslwr(char *string)
{
  unsigned __int8 v2; // [sp+0h] [bp-10h]@10
  int retval; // [sp+4h] [bp-Ch]@4
  char ret[4]; // [sp+8h] [bp-8h]@4
  char *cp; // [sp+Ch] [bp-4h]@1

  _lock(25);
  for ( cp = string; *cp; ++cp )
  {
    if ( byte_10265061[(unsigned __int8)*cp] & 4 )
    {
      retval = __crtLCMapStringA(__mblcid, 0x100u, cp, 2, ret, 2, __mbcodepage, 1);
      if ( !retval )
      {
        _unlock(25);
        return 0;
      }
      *cp = ret[0];
      if ( retval > 1 )
        *++cp = ret[1];
    }
    else
    {
      if ( (byte_10265061[(unsigned __int8)*cp] & 0x10) == 0x10 )
        v2 = _mbcasemap[(unsigned __int8)*cp];
      else
        v2 = *cp;
      *cp = v2;
    }
  }
  _unlock(25);
  return string;
}

而STL調(diào)用 MSVCRT(D).dll的int tolower( intc );

int __cdecl tolower(int c)
{
  int result; // eax@5
  int local_lock_flag; // [sp+0h] [bp-4h]@7
  int ca; // [sp+Ch] [bp+8h]@9

  if ( dword_10264B24 )
  {
    InterlockedIncrement(&__unguarded_readlc_active);
    if ( __setlc_active )
    {
      InterlockedDecrement(&__unguarded_readlc_active);
      _lock(19);
      local_lock_flag = 1;
    }
    else
    {
      local_lock_flag = 0;
    }
    ca = _tolower_lk(c);
    if ( local_lock_flag )
      _unlock(19);
    else
      InterlockedDecrement(&__unguarded_readlc_active);
    result = ca;
  }
  else
  {
    if ( c >= 65 && c <= 90 )
      c += 32;
    result = c;
  }
  return result;
}

相關(guān)鏈接：

https://social.msdn.microsoft.com/Forums/vstudio/zh-CN/65f0347a-5ed7-4ddb-8439-1b7989b4c14d/cstringmakelower-chinese-windows-crash?forum=vclanguage