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32 .\" @(#)unvis.3 8.2 (Berkeley) 12/11/93
41 .Nd decode a visual representation of characters
45 .Fn unvis "char *cp" "int c" "int *astate" "int flag"
47 .Fn strunvis "char *dst" "const char *src"
54 are used to decode a visual representation of characters, as produced
58 the original form. Unvis is called with successive characters in
61 sequence is recognized, at which time the decoded character is
62 available at the character pointed to by
65 characters pointed to by
67 into the buffer pointed to by
77 decoding any escape sequences along the way,
78 and returns the number of characters placed into
81 invalid escape sequence was detected. The size of
86 (that is, no expansion takes place during
92 implements a state machine that can be used to decode an arbitrary
93 stream of bytes. All state associated with the bytes being decoded
96 function (that is, a pointer to the state is passed in), so
97 calls decoding different streams can be freely intermixed. To
98 start decoding a stream of bytes, first initialize an integer
101 with each successive byte, along with a pointer
102 to this integer, and a pointer to a destination character.
106 has several return codes that must be handled properly. They are:
107 .Bl -tag -width UNVIS_VALIDPUSH
109 Another character is necessary; nothing has been recognized yet.
111 A valid character has been recognized and is available at the location
113 .It Dv UNVIS_VALIDPUSH
114 A valid character has been recognized and is available at the location
115 pointed to by cp; however, the character currently passed in should
118 A valid sequence was detected, but no character was produced. This
119 return code is necessary to indicate a logical break between characters.
121 An invalid escape sequence was detected, or the decoder is in an
122 unknown state. The decoder is placed into the starting state.
125 When all bytes in the stream have been processed, call
127 one more time with flag set to
129 to extract any remaining character (the character passed in is ignored).
131 The following code fragment illustrates a proper use of
133 .Bd -literal -offset indent
137 while ((ch = getchar()) != EOF) {
139 switch(unvis(&out, ch, &state, 0)) {
146 case UNVIS_VALIDPUSH:
150 (void)fprintf(stderr, "bad sequence!\n");
154 if (unvis(&out, (char)0, &state, UNVIS_END) == UNVIS_VALID)