Node:Unreading Idea, Next:How Unread, Up:Unreading

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.