以只读方式打开，放置在文件开头的文件指针。
Open for reading only; place the file pointer at the beginning of the file.
注：fopen中使用的“r ”将指示文件以只读方式打开。
Note: the "r" used in fopen indicates that the file is open for reading only.
然后，你可以选择启用应用重做或者实时应用，再或者以只读方式打开数据库来访问。
You then have the option of either starting Redo apply or real-time apply, or opening the database for read-only access.
以只读方式打开物理备库可以延长失败或中断恢复的时间，因为数据库必须在故障切换后重新启动。
Opening the physical standby database read-only may lengthen the time it takes to recover from a failure or outage, because the database must be restarted after a failover.
函数尝试使用错误的文件描述符（例如，它不引用打开的文件，或者用于尝试写入以只读方式打开的文件）。
EBADF -- A function tried to use a bad file descriptor (it doesn't refer to an open file, for example, or it was used in an attempt to write to a file that was opened read-only).
与共享内存对象相似，对于以只读方式打开消息队列，应该把open_only属性传递给构造函数。
Similar to the case for a Shared memory object, a message queue that is opened only for reading will have the open_only attribute passed in the constructor.
与共享内存对象相似，对于以只读方式打开消息队列，应该把open_only属性传递给构造函数。
Similar to the case for a Shared memory object, a message queue that is opened only for reading will have the open_only attribute passed in the constructor.
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