NAME¶
unvis
,
strunvis
,
strnunvis
—
decode a visual representation of characters
LIBRARY¶
library “libbsd”
SYNOPSIS¶
#include
<bsd/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);
DESCRIPTION¶
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
() function 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.
RETURN VALUES¶
The
unvis
() function has several return codes
that must be handled properly. They are:
0
(zero)
- Another character is necessary; nothing has been recognized 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 produced. This return
code is necessary to indicate a logical 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.
EXAMPLES¶
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);
SEE ALSO¶
unvis(1),
vis(1),
vis(3)
HISTORY¶
The
unvis
() function first appeared in
4.4BSD.