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[dragonfly.git] / lib / libc / gen / unvis.3
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1.\" Copyright (c) 1989, 1991, 1993
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32.\" @(#)unvis.3 8.2 (Berkeley) 12/11/93
33.\" $FreeBSD: src/lib/libc/gen/unvis.3,v 1.6.2.5 2001/12/14 18:33:51 ru Exp $
1de703da 34.\" $DragonFly: src/lib/libc/gen/unvis.3,v 1.2 2003/06/17 04:26:42 dillon Exp $
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35.\"
36.Dd December 11, 1993
37.Dt UNVIS 3
38.Os
39.Sh NAME
40.Nm unvis ,
41.Nm strunvis
42.Nd decode a visual representation of characters
43.Sh LIBRARY
44.Lb libc
45.Sh SYNOPSIS
46.In vis.h
47.Ft int
48.Fn unvis "char *cp" "int c" "int *astate" "int flag"
49.Ft int
50.Fn strunvis "char *dst" "const char *src"
51.Sh DESCRIPTION
52The
53.Fn unvis
54and
55.Fn strunvis
56functions
57are used to decode a visual representation of characters, as produced
58by the
59.Xr vis 3
60function, back into
61the original form. Unvis is called with successive characters in
62.Ar c
63until a valid
64sequence is recognized, at which time the decoded character is
65available at the character pointed to by
66.Ar cp .
67Strunvis decodes the
68characters pointed to by
69.Ar src
70into the buffer pointed to by
71.Ar dst .
72.Pp
73The
74.Fn strunvis
75function
76simply copies
77.Ar src
78to
79.Ar dst ,
80decoding any escape sequences along the way,
81and returns the number of characters placed into
82.Ar dst ,
83or \-1 if an
84invalid escape sequence was detected. The size of
85.Ar dst
86should be
87equal to the size of
88.Ar src
89(that is, no expansion takes place during
90decoding).
91.Pp
92The
93.Fn unvis
94function
95implements a state machine that can be used to decode an arbitrary
96stream of bytes. All state associated with the bytes being decoded
97is stored outside the
98.Fn unvis
99function (that is, a pointer to the state is passed in), so
100calls decoding different streams can be freely intermixed. To
101start decoding a stream of bytes, first initialize an integer
102to zero. Call
103.Fn unvis
104with each successive byte, along with a pointer
105to this integer, and a pointer to a destination character.
106The
107.Fn unvis
108function
109has several return codes that must be handled properly. They are:
110.Bl -tag -width UNVIS_VALIDPUSH
111.It Li \&0 (zero)
112Another character is necessary; nothing has been recognized yet.
113.It Dv UNVIS_VALID
114A valid character has been recognized and is available at the location
115pointed to by cp.
116.It Dv UNVIS_VALIDPUSH
117A valid character has been recognized and is available at the location
118pointed to by cp; however, the character currently passed in should
119be passed in again.
120.It Dv UNVIS_NOCHAR
121A valid sequence was detected, but no character was produced. This
122return code is necessary to indicate a logical break between characters.
123.It Dv UNVIS_SYNBAD
124An invalid escape sequence was detected, or the decoder is in an
125unknown state. The decoder is placed into the starting state.
126.El
127.Pp
128When all bytes in the stream have been processed, call
129.Fn unvis
130one more time with
131.Ar flag
132set to
133.Dv UNVIS_END
134to extract any remaining character (the character passed in is ignored).
135.Pp
136The following code fragment illustrates a proper use of
137.Fn unvis .
138.Bd -literal -offset indent
139int state = 0;
140char out;
141
142while ((ch = getchar()) != EOF) {
143again:
144 switch(unvis(&out, ch, &state, 0)) {
145 case 0:
146 case UNVIS_NOCHAR:
147 break;
148 case UNVIS_VALID:
149 (void) putchar(out);
150 break;
151 case UNVIS_VALIDPUSH:
152 (void) putchar(out);
153 goto again;
154 case UNVIS_SYNBAD:
155 (void)fprintf(stderr, "bad sequence!\en");
156 exit(1);
157 }
158}
159if (unvis(&out, (char)0, &state, UNVIS_END) == UNVIS_VALID)
160 (void) putchar(out);
161.Ed
162.Sh SEE ALSO
163.Xr vis 1
164.Sh HISTORY
165The
166.Fn unvis
167function
168first appeared in
169.Bx 4.4 .