peek-byte

Arguments: stream &optional (eof-error-p t)eof-value

This one-byte analog of peek-char is similar to read-byte, but if the result of the read does not cause an eof condition the octet is put back again. If it returns, peek-byte returns either the next octet to be read or the eof-value if at eof. Note that peek-byte is not as complex as peek-char, since there is no concept of whitespace characters when characters are not involved.

As with peek-char, if an eof is read, an error is signaled if eof-error-p is true, otherwise eof-value is returned.

peek-byte is essentially equivalent to a read-byte followed by a possible unread-byte. Unlike unread-byte, peek-byte is guaranteed to work under all normal circumstances (including at eof).

peek-byte currently does not work in Gray streams - error is called when peek-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 unread-byte.

Copyright (c) 1998-2019, Franz Inc. Oakland, CA., USA. All rights reserved.
This page is new in the 9.0 release.
Created 2019.8.20.