windows - 如何从 ReOpenFile 的 QFile 或 QSaveFile 获取窗口句柄？

Question

给定一个 QFileDevice 实例(一个 QFile 或 QSaveFile)——如何获得 native Windows HANDLE 文件？这个句柄可以与 ReOpenFile 一起使用吗？

Answer 1

QFileDevice::handle()返回从 QFSFileEnginePrivate::nativeHandle 获得的 C 文件描述符(fd - 一个小整数) .该文件描述符是您从 _open_osfhandle 中获得的内容.您需要使用 _get_osfhandle返回到 HANDLE。

struct FdHandle {
  int fd = -1;
  HANDLE handle = INVALID_HANDLE_VALUE;
  operator HANDLE() const { return handle; }
  bool isFdValid() const { return fd != -1; }
  bool isHandleValid() const { return handle != INVALID_HANDLE_VALUE; }
};

FdHandle windowsHandleOf(QFileDevice* dev) {
  auto fd = dev->handle(); 
  return {fd, (HANDLE)_get_osfhandle(fd)};
}

ReOpenFile可能会返回不同的文件句柄，因此您可能需要为它重新打开文件。重载的 ReOpenFile 处理它:

struct ReOpenResult {
  enum { OK = 0, FileClosed = 10, NoHandle = 20, 
         OldHandle = 30, OpenFailed = 40 } rc;
  HANDLE handle = INVALID_HANDLE_VALUE;
  operator HANDLE() const { return handle; }
  explicit operator bool() const { return rc == OK; }
  bool isHandleValid() const { return handle != INVALID_HANDLE_VALUE; }
};

ReOpenResult ReOpenFile(QFile *file, DWORD access, DWORD shareMode, DWORD flags) {
  if (!file->isOpen())
    return {ReOpenResult::FileClosed};
  auto oldHandle = windowsHandleOf(file);
  if (oldHandle == INVALID_HANDLE_VALUE)
    return {ReOpenResult::NoHandle};
  auto newHandle = ReOpenFile(oldHandle, access, shareMode, flags);
  if (newHandle == INVALID_HANDLE_VALUE)
    return {ReOpenResult::OldHandle, oldHandle};
  if (!open(file, file->openMode(), newHandle))
    return {ReOpenResult::OpenFailed, oldHandle};
  return {ReOpenResult::OK, newHandle};
}

采用HANDLE 的“缺​​失”open 是:

struct OpenResult {
  enum { OK = 0, SameHandleOK = 1, InvalidHandle = 10, CCloseFailed = 20,
         InvalidFd = 30, OpenFailed = 40 } rc = OK;
  explicit operator bool() const { return rc < InvalidHandle; };
};

OpenResult open(QFile* file, QIODevice::OpenMode mode, HANDLE handle) {
  if (handle == INVALID_HANDLE_VALUE)
    return {OpenResult::InvalidHandle};
  if (file->isOpen() && windowsHandleOf(file) == handle)
    return {OpenResult::SameHandleOK};
  file->close();
  if (auto fd = file->handle() != -1)
    if (_close(fd)) // the C handle is still open, don't leak it
      return {OpenResult::CCloseFailed};
  int flags = 0;
  if (mode & QIODevice::Append)
    flags |= _O_APPEND;
  if (!(mode & QIODevice::WriteOnly))
    flags |= _O_RDONLY;
  auto fd = _open_osfhandle((intptr_t)handle, flags);
  if (fd == -1)
    return {OpenResult::InvalidFd};
  if (!file->open(fd, mode, QFileDevice::AutoCloseHandle))
    return {OpenResult::OpenFailed};
  return {};
}