C++ stringT::clear方法代码示例

bool pws_os::LockFile(const stringT &filename, stringT &locker, 
                      HANDLE &lockFileHandle, int &LockCount)
{
  const stringT lock_filename = GetLockFileName(filename);
  stringT s_locker;
  const stringT user = pws_os::getusername();
  const stringT host = pws_os::gethostname();
  const stringT pid = pws_os::getprocessid();

  // Use Win32 API for locking - supposedly better at
  // detecting dead locking processes
  if (lockFileHandle != INVALID_HANDLE_VALUE) {
    // here if we've open another (or same) dbase previously,
    // need to unlock it. A bit inelegant...
    // If app was minimized and ClearData() called, we've a small
    // potential for a TOCTTOU issue here. Worse case, lock
    // will fail.

    const stringT cs_me = user + _T("@") + host + _T(":") + pid;
    GetLocker(lock_filename, s_locker);

    if (cs_me == s_locker) {
      LockCount++;
      locker.clear();
      return true;
    } else {
      pws_os::UnlockFile(filename, lockFileHandle, LockCount);
    }
  }

  // Since ::CreateFile can't create directories, we need to check it exists
  // first and, if not, try and create it.
  // This is primarily for the config directory in the local APPDATA directory
  // but will also be called for the database lock file - and since the database
  // is already there, it is a bit of a redundant check but easier than coding
  // for every different situation.
  stringT sDrive, sDir, sName, sExt;
  pws_os::splitpath(lock_filename, sDrive, sDir, sName, sExt);
  stringT sNewDir = sDrive + sDir;
	DWORD dwAttrib = GetFileAttributes(sNewDir.c_str());
  DWORD dwerr(0);
  if (dwAttrib == INVALID_FILE_ATTRIBUTES)
    dwerr = GetLastError();

  BOOL brc(TRUE);
  if (dwerr == ERROR_FILE_NOT_FOUND || 
      (dwAttrib != INVALID_FILE_ATTRIBUTES) &&
      !(dwAttrib & FILE_ATTRIBUTE_DIRECTORY)) {
    SECURITY_ATTRIBUTES secatt = {0};
    secatt.nLength = sizeof(secatt);
    brc = ::CreateDirectory(sNewDir.c_str(), &secatt);
  }

  // Obviously, if we can't create the directory - don't bother trying to
  // create the lock file!
  if (brc) {
    lockFileHandle = ::CreateFile(lock_filename.c_str(),
                                  GENERIC_WRITE,
                                  FILE_SHARE_READ,
                                  NULL,
                                  CREATE_ALWAYS, // rely on share to fail if exists!
                                  FILE_ATTRIBUTE_NORMAL | FILE_FLAG_WRITE_THROUGH | 
                                  // (Lockheed Martin) Secure Coding  11-14-2007
                                  SECURITY_SQOS_PRESENT | SECURITY_IDENTIFICATION,
                                  NULL);

    // Make sure it's a file and not a pipe.  (Lockheed Martin) Secure Coding  11-14-2007
    if (lockFileHandle != INVALID_HANDLE_VALUE) {
      if (::GetFileType( lockFileHandle ) != FILE_TYPE_DISK) {
        ::CloseHandle( lockFileHandle );
        lockFileHandle = INVALID_HANDLE_VALUE;
      }
    }
    // End of Change.  (Lockheed Martin) Secure Coding  11-14-2007
  }

  if (lockFileHandle == INVALID_HANDLE_VALUE) {
    DWORD error = GetLastError();
    switch (error) {
    case ERROR_SHARING_VIOLATION: // already open by a live process
      GetLocker(lock_filename, s_locker);
      locker = s_locker.c_str();
      break;
    default: {
      // Give detailed error message, if possible
      LPTSTR lpMsgBuf = NULL;
      if (FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
                        NULL,
                        error,
                        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                        (LPTSTR)&lpMsgBuf,
                        0, NULL) != 0) {
        locker = lpMsgBuf;
        LocalFree(lpMsgBuf);
      } else { // should never happen!
        LoadAString(locker, IDSC_NOLOCKACCESS); // berrer than nothing
      }
    }
      break;
    } // switch (error)
//.........这里部分代码省略.........