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32 .\" From: @(#)vis.3 8.1 (Berkeley) 6/9/93
33 .\" $FreeBSD: src/lib/libc/gen/vis.3,v 1.8.2.6 2001/12/14 18:33:51 ru Exp $
40 .Nd visually encode characters
46 .Fn vis "char *dst" "int c" "int flag" "int nextc"
48 .Fn strvis "char *dst" "const char *src" "int flag"
50 .Fn strvisx "char *dst" "const char *src" "size_t len" "int flag"
57 a string which represents the character
61 needs no encoding, it is copied in unaltered. The string is
62 null terminated, and a pointer to the end of the string is
63 returned. The maximum length of any encoding is four
64 characters (not including the trailing
67 encoding a set of characters into a buffer, the size of the buffer should
68 be four times the number of characters encoded, plus one for the trailing
70 The flag parameter is used for altering the default range of
71 characters considered for encoding and for altering the visual
73 The additional character,
75 is only used when selecting the
77 encoding format (explained below).
85 a visual representation of
90 function encodes characters from
97 function encodes exactly
102 is useful for encoding a block of data that may contain
110 must be four times the number
111 of characters encoded from
116 forms return the number of characters in dst (not including
120 The encoding is a unique, invertible representation composed entirely of
121 graphic characters; it can be decoded back into the original form using
128 There are two parameters that can be controlled: the range of
129 characters that are encoded, and the type
130 of representation used.
131 By default, all non-graphic characters
132 except space, tab, and newline are encoded.
137 .Bl -tag -width VIS_WHITEX
152 Only encode "unsafe" characters. Unsafe means control
153 characters which may cause common terminals to perform
154 unexpected functions. Currently this form allows space,
155 tab, newline, backspace, bell, and return - in addition
156 to all graphic characters - unencoded.
159 There are four forms of encoding.
160 Most forms use the backslash character
162 to introduce a special
163 sequence; two backslashes are used to represent a real backslash.
164 These are the visual formats:
165 .Bl -tag -width VIS_HTTPSTYLE
169 to represent meta characters (characters with the 8th
170 bit set), and use carat
172 to represent control characters see
173 .Pf ( Xr iscntrl 3 ) .
174 The following formats are used:
175 .Bl -tag -width xxxxx
177 Represents the control character
190 with the 8th bit set.
196 Represents control character
198 with the 8th bit set.
212 Represents Meta-space.
216 Use C-style backslash sequences to represent standard non-printable
218 The following sequences are used to represent the indicated characters:
219 .Bd -unfilled -offset indent
220 .Li \ea Tn - BEL No (007)
221 .Li \eb Tn - BS No (010)
222 .Li \ef Tn - NP No (014)
223 .Li \en Tn - NL No (012)
224 .Li \er Tn - CR No (015)
225 .Li \et Tn - HT No (011)
226 .Li \ev Tn - VT No (013)
227 .Li \e0 Tn - NUL No (000)
230 When using this format, the nextc parameter is looked at to determine
233 character can be encoded as
239 is an octal digit, the latter representation is used to
242 Use URI encoding as described in RFC 1808.
247 represents a hexadecimal digit.
249 Use a three digit octal sequence. The form is
253 represents an octal digit.
256 There is one additional flag,
259 doubling of backslashes and the backslash before the default
260 format (that is, control characters are represented by
265 With this flag set, the encoding is
266 ambiguous and non-invertible.
272 .%T Relative Uniform Resource Locators
276 These functions first appeared in