UNVIS(3) BSD Programmer's Manual UNVIS(3)
unvis, strunvis, strnunvis - decode a visual representation of characters
#include <vis.h>
int
unvis(char *cp, char c, int *astate, int flag);
int
strunvis(char *dst, char *src);
ssize_t
strnunvis(char *dst, char *src, size_t size);
The unvis(), strunvis() and strnunvis() functions are used to decode a
visual representation of characters, as produced by the vis(3) function,
back into the original form. unvis() is called with successive characters
in c until a valid sequence is recognized, at which time the decoded
character is available at the character pointed to by cp.
strunvis() decodes the characters pointed to by src into the buffer
pointed to by dst.
strnunvis() decodes the characters pointed to by src into the buffer
pointed to by dst, writing a maximum of size bytes. The strunvis() func-
tion simply copies src to dst, decoding any escape sequences along the
way, and returns the number of characters placed into dst, or -1 if an
invalid escape sequence was detected. The size of dst should be equal to
the size of src (that is, no expansion takes place during decoding).
strunvis() terminates the destination string with a trailing NUL byte;
strnunvis() does so if size is larger than 0.
The unvis() function implements a state machine that can be used to
decode an arbitrary stream of bytes. All state associated with the bytes
being decoded is stored outside the unvis() function (that is, a pointer
to the state is passed in), so calls decoding different streams can be
freely intermixed. To start decoding a stream of bytes, first initialize
an integer to zero. Call unvis() with each successive byte, along with a
pointer to this integer, and a pointer to a destination character.
The unvis() function has several return codes that must be handled prop-
erly. They are:
0 (zero) Another character is necessary; nothing has been recog-
nized yet.
UNVIS_VALID A valid character has been recognized and is available
at the location pointed to by cp.
UNVIS_VALIDPUSH A valid character has been recognized and is available
at the location pointed to by cp; however, the character
currently passed in should be passed in again.
UNVIS_NOCHAR A valid sequence was detected, but no character was pro-
duced. This return code is necessary to indicate a logi-
cal break between characters.
UNVIS_SYNBAD An invalid escape sequence was detected, or the decoder
is in an unknown state. The decoder is placed into the
starting state.
When all bytes in the stream have been processed, call unvis() one more
time with flag set to UNVIS_END to extract any remaining character (the
character passed in is ignored).
The strunvis() function returns the number of bytes written (not counting
the trailing NUL byte) or -1 if an error occurred.
The strnunvis() function returns the number of bytes (not counting the
trailing NUL byte) that would be needed to fully convert the input
string, or -1 if an error occurred.
The following code fragment illustrates a proper use of unvis().
int state = 0;
char out;
while ((ch = getchar()) != EOF) {
again:
switch(unvis(&out, ch, &state, 0)) {
case 0:
case UNVIS_NOCHAR:
break;
case UNVIS_VALID:
(void) putchar(out);
break;
case UNVIS_VALIDPUSH:
(void) putchar(out);
goto again;
case UNVIS_SYNBAD:
(void)fprintf(stderr, "bad sequence!\n");
exit(1);
}
}
if (unvis(&out, (char)0, &state, UNVIS_END) == UNVIS_VALID)
(void) putchar(out);
unvis(1), vis(1), vis(3)
The unvis() function first appeared in 4.4BSD.
MirBSD #10-current December 11, 1993 1