unread-byte

Arguments: stream

This function is similar to unread-char, but it backs up to the previous octet rather than character. It is also similar in that if unread-byte is called immediately after a "back-up" function (i.e. peek-char/peek-byte or unread-char/unread-byte) it may fail. However, it need not fail; if the stream being operated on is not currently positioned at the beginning of its buffer, even after a backup function has just been called, then unread-byte may still succeed. There is currently no portable way to know whether an unread-byte will work, unless the last operation on the stream was a read operation other than a back-up function.

unread-byte currently does not work on Gray streams - error is called when unread-byte is called on a Gray stream. (Gray streams are discussed in gray-streams.htm.)

See peek-byte and unread-byte in streams.htm for a general discussion of this function and the related peek-byte.

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This page is new in the 9.0 release.
Created 2019.8.20.