If not NULL, increment the line counter.
如果不是NULL，则增加行计数器。
The logic used for form-feed-delimited pages is roughly the same, but slightly simpler, as there is no need for a line counter: Read char by char using the getc library function.
用于换页定界的页的逻辑大体上相同，只是稍稍简单一些，因为不需要行计数器：使用getc库函数逐个读取字符。
I think I must have left it by your air-line counter at the airport.
我想我肯定把它忘在机场你们航空公司的柜台边上了。
I think I must have left it by your air-line counter at the airport.
我想我肯定把它忘在机场你们航空公司的柜台边上了。
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