用红宝石写入文件的中间 [英] writing to the middle of a file in ruby

问题描述

我用a +选项打开了一个红宝石文件。我可以找到文件的中间并从中读取，但是当我尝试写入文件时，总是进行到最后。

  jpg = File.new（/ tmp / bot.jpg，如何写入中间位置？ a +）
 jpg.seek 24 
 puts jpg.getc.chr 
 jpg.seek 24 
 jpg.writeR
 jpg.seek 28 
 jpg.writeW
 puts jpg.pos 
 jpg.close 
  

< R和W都在文件末尾。

我知道我只能覆盖现有的字节，没关系，那就是我想要的 c>模式：确保所有的写入操作总是进行到最后，同时允许读取和查找（当然，在给定模式的情况下，只对读取有意义）。使用r +，如果您不希望所有的写入操作都一​​直到最后。

I've opened a file in ruby with the options a+. I can seek to the middle of the file and read from it but when I try to write the writes always go to the end. How do I write to a position in the middle?

jpg = File.new("/tmp/bot.jpg", "a+")
jpg.seek 24
puts jpg.getc.chr
jpg.seek 24
jpg.write "R" 
jpg.seek 28
jpg.write "W" 
puts jpg.pos
jpg.close

The R and W both end up at the end of the file.

I know I can only overwrite existing bytes, that is ok, that is what I want to do.

解决方案

This behavior is exactly what you request with the "a+" mode: ensure all writes always go to the end, while allowing reading and seeking (seeking only meaningful for reading of course, given the mode). Use "r+" if you don't want all writes to always go to the end.

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