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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 $
34 .\" $DragonFly: src/lib/libc/gen/vis.3,v 1.2 2003/06/17 04:26:42 dillon Exp $
41 .Nd visually encode characters
47 .Fn vis "char *dst" "int c" "int flag" "int nextc"
49 .Fn strvis "char *dst" "const char *src" "int flag"
51 .Fn strvisx "char *dst" "const char *src" "size_t len" "int flag"
58 a string which represents the character
62 needs no encoding, it is copied in unaltered. The string is
63 null terminated, and a pointer to the end of the string is
64 returned. The maximum length of any encoding is four
65 characters (not including the trailing
68 encoding a set of characters into a buffer, the size of the buffer should
69 be four times the number of characters encoded, plus one for the trailing
71 The flag parameter is used for altering the default range of
72 characters considered for encoding and for altering the visual
74 The additional character,
76 is only used when selecting the
78 encoding format (explained below).
86 a visual representation of
91 function encodes characters from
98 function encodes exactly
103 is useful for encoding a block of data that may contain
111 must be four times the number
112 of characters encoded from
117 forms return the number of characters in dst (not including
121 The encoding is a unique, invertible representation composed entirely of
122 graphic characters; it can be decoded back into the original form using
129 There are two parameters that can be controlled: the range of
130 characters that are encoded, and the type
131 of representation used.
132 By default, all non-graphic characters
133 except space, tab, and newline are encoded.
138 .Bl -tag -width VIS_WHITEX
153 Only encode "unsafe" characters. Unsafe means control
154 characters which may cause common terminals to perform
155 unexpected functions. Currently this form allows space,
156 tab, newline, backspace, bell, and return - in addition
157 to all graphic characters - unencoded.
160 There are four forms of encoding.
161 Most forms use the backslash character
163 to introduce a special
164 sequence; two backslashes are used to represent a real backslash.
165 These are the visual formats:
166 .Bl -tag -width VIS_HTTPSTYLE
170 to represent meta characters (characters with the 8th
171 bit set), and use carat
173 to represent control characters see
174 .Pf ( Xr iscntrl 3 ) .
175 The following formats are used:
176 .Bl -tag -width xxxxx
178 Represents the control character
191 with the 8th bit set.
197 Represents control character
199 with the 8th bit set.
213 Represents Meta-space.
217 Use C-style backslash sequences to represent standard non-printable
219 The following sequences are used to represent the indicated characters:
220 .Bd -unfilled -offset indent
221 .Li \ea Tn - BEL No (007)
222 .Li \eb Tn - BS No (010)
223 .Li \ef Tn - NP No (014)
224 .Li \en Tn - NL No (012)
225 .Li \er Tn - CR No (015)
226 .Li \et Tn - HT No (011)
227 .Li \ev Tn - VT No (013)
228 .Li \e0 Tn - NUL No (000)
231 When using this format, the nextc parameter is looked at to determine
234 character can be encoded as
240 is an octal digit, the latter representation is used to
243 Use URI encoding as described in RFC 1808.
248 represents a hexadecimal digit.
250 Use a three digit octal sequence. The form is
254 represents an octal digit.
257 There is one additional flag,
260 doubling of backslashes and the backslash before the default
261 format (that is, control characters are represented by
266 With this flag set, the encoding is
267 ambiguous and non-invertible.
273 .%T Relative Uniform Resource Locators
277 These functions first appeared in