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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 $
41 .Nd decode a visual representation of characters
47 .Fn unvis "char *cp" "int c" "int *astate" "int flag"
49 .Fn strunvis "char *dst" "const char *src"
56 are used to decode a visual representation of characters, as produced
60 the original form. Unvis is called with successive characters in
63 sequence is recognized, at which time the decoded character is
64 available at the character pointed to by
67 characters pointed to by
69 into the buffer pointed to by
79 decoding any escape sequences along the way,
80 and returns the number of characters placed into
83 invalid escape sequence was detected. The size of
88 (that is, no expansion takes place during
94 implements a state machine that can be used to decode an arbitrary
95 stream of bytes. All state associated with the bytes being decoded
98 function (that is, a pointer to the state is passed in), so
99 calls decoding different streams can be freely intermixed. To
100 start decoding a stream of bytes, first initialize an integer
103 with each successive byte, along with a pointer
104 to this integer, and a pointer to a destination character.
108 has several return codes that must be handled properly. They are:
109 .Bl -tag -width UNVIS_VALIDPUSH
111 Another character is necessary; nothing has been recognized yet.
113 A valid character has been recognized and is available at the location
115 .It Dv UNVIS_VALIDPUSH
116 A valid character has been recognized and is available at the location
117 pointed to by cp; however, the character currently passed in should
120 A valid sequence was detected, but no character was produced. This
121 return code is necessary to indicate a logical break between characters.
123 An invalid escape sequence was detected, or the decoder is in an
124 unknown state. The decoder is placed into the starting state.
127 When all bytes in the stream have been processed, call
133 to extract any remaining character (the character passed in is ignored).
135 The following code fragment illustrates a proper use of
137 .Bd -literal -offset indent
141 while ((ch = getchar()) != EOF) {
143 switch(unvis(&out, ch, &state, 0)) {
150 case UNVIS_VALIDPUSH:
154 (void)fprintf(stderr, "bad sequence!\en");
158 if (unvis(&out, (char)0, &state, UNVIS_END) == UNVIS_VALID)