A file designator.
If direction is
:probe, external-format is ignored. The element type and external format of the returned stream are undefined.
By default, the value of *default-character-element-type* (the ANSI standard default is
An external file format designator. By default, this is
What to do if the file stream already exists. The possible values for this are as in the ANSI standard.
What to do if the file stream does not already exist. The possible values for this are as in the ANSI standard.
Otherwise, the system decides which external format to use via guess-external-format. By default, this finds a match based on the filename; or (if that fails), looks in the EMACS-style (
-*-) attribute line for an option called
coding; or (if that fails), chooses from among likely encodings by analyzing the bytes near the start of the file. By default, it then also analyzes the start of the file for byte patterns indicating the end-of-line style, and uses a default end-of-line style if no such pattern is found. This behavior is configurable.
After the external-format has been determined, it is verified using valid-external-format-p; and an error is signaled if this check fails.
:default as its element-type arg, it chooses the type on the basis of the external format. If
open gets an element-type other than
:default and the direction is
:io, the argument must be a supertype of the type of characters produced by the external format; if the direction is
:io, it must be a subtype of the type of characters accepted by the external format; if it does not satisfy these requirements, an error is signaled.
Standard stream input and output functions for character and binary data generally work in the obvious way on a
file-stream with element-type
(unsigned-byte 8) or
(signed-byte 8). For example,
read-sequence can be called with a string buffer and a binary
file-stream: the character data is constructed from the input as if by
write-sequence can be called with a string buffer and a binary
file-stream: the output is converted from the character data as if by
char-code. Also, 8-bit binary data can be read from and written to a
LispWorks User Guide and Reference Manual - 20 Sep 2017