selpg通过以下方法记住当前页号：如果输入是每页行数固定的，则selpg统计新行数，直到达到页长度后增加页计数器。

Selpg keeps track of the current page number as follows: If input is fixed-lines-per-page, it counts newlines until the page length is reached and increments a page counter.

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为每一行数据所创建的索引成为了计数器，因为每当新的一行数据加进来的时候，这个索引是唯一的增量，这也意味着计数器将与字符串数据的总量同步变化。

The index created for each row of data becomes the count because it was only incremented when a new row of data was found, meaning it is in sync with the amount of data in the string.

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