MFC在多字节环境下计算unicode串长度和截断中文字符

CString CmuchbyteDlg::GetChinese(int size,CString &str)
{

 DWORD dBufSize = MultiByteToWideChar(CP_ACP, 0, str, str.GetLength(), NULL, 0);

 wchar_t * dBuf=new wchar_t[dBufSize];
 //初始化
 wmemset(dBuf,0,dBufSize);

 int nRet = MultiByteToWideChar(CP_ACP, 0, str,  str.GetLength(), dBuf, dBufSize);

 CString Ansstr = "";
 int ans = 0;
 for(int i = 0;i < nRet;i++)
 {
  if(dBuf[i] < 0 || dBuf[i] > 0x80)
  {
   if(ans >= size)
    break;
   ans ++;
   CString cstring(dBuf[i]);
   Ansstr += cstring;
  }
 }
 return Ansstr;
}