Google Protocol Buffers，在提供的流对象中向后重新定位 IO 头 [英] Google Protocol Buffers, backward reposition IO head in the stream objects provided

问题描述

我想将 IO 头移动到某个 CodedOutputStream 或 ZeroCopyOutputStream 的开头，以便我可以使用文件中有多少 protobuf 消息以及以下消息消耗多少字节来更新头数据结构.

I want to move the IO head to the start of a certain CodedOutputStream or ZeroCopyOutputStream so I can update a header data structure with how many protobuf messages are in the file, and how many bytes the following messages consume.

备份功能 不是为此而设计的，有什么建议吗?我正在为事件数据创建文件格式，其中每个文件包含多个事件数据集.我需要两种类型的标头实体(固定大小)一个是全局的，一个是每个数据集的.我在写入数据集事件后更新这些.那么，如何在不破坏流对象的内部状态的情况下移动写入标头?.

The Backup function is not intended for this, any suggestions ? I am creating a file format for event data, where each file contains multiple event data-sets. I need 2 types of header entities for this (fixed size)A global one, and a per data-set one. I update these after writing in the data-set events. So, How do I move the write header without corrupting the internal state of the stream objects ?.

编辑

我想知道，如果我刷新流包装器并仅使用 c 函数来重新安装头部，这是否适用于流类，还是最终会处于未定义的状态?

I wonder, if I flush the stream wrappers and just use the c functions to reseat the head, will this work for the stream classes, or will I end up in undefined land ?

推荐答案

我想最明显的方法是有两个文件而不是每个文件:带有流数据的主文件，然后是带有标题的索引文件信息.

I guess the most obvious way would be to have two files instead of each one: The main file with the streamed data, and then an index file with the header information.

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