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What Unreading Means

Here is a pictorial explanation of unreading. Suppose you have a stream reading a file that contains just six characters, the letters `foobar'. Suppose you have read three characters so far. The situation looks like this:

f  o  o  b  a  r
         ^

so the next input character will be `b'.

If instead of reading `b' you unread the letter `o', you get a situation like this:

f  o  o  b  a  r
         |
      o--
      ^

so that the next input characters will be `o' and `b'.

If you unread `9' instead of `o', you get this situation:

f  o  o  b  a  r
         |
      9--
      ^

so that the next input characters will be `9' and `b'.

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