NAME
unvis, strunvis,
strnunvis —
decode a visual representation of
characters
SYNOPSIS
#include
<vis.h>
int
unvis(char
*cp, char c,
int *astate,
int flag);
int
strunvis(char
*dst, const char
*src);
ssize_t
strnunvis(char
*dst, const 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
HISTORY
The unvis() function first appeared in
4.4BSD.