cdecode -> unvis - new man page

[unix-history] / usr / src / lib / libc / gen / unvis.3

.\" Copyright (c) 1989 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" %sccs.include.redist.man%
.\"
.\"     @(#)unvis.3     1.2 (Berkeley) %G%
.\"
.TH UNVIS 3 ""
.UC 7
.SH NAME
unvis, strunvis - decode a visual representation of characters
.SH SYNOPSIS
.nf
.ft B
#include <vis.h>

int unvis(cp, c, astate, flag)
u_char *cp, c;
int *astate, flag;

int strunvis(dst, src)
char *dst, *src;

.ft R
.fi
.SH DESCRIPTION
.I Unvis
and
.I strunvis
are used to decode a visual representation of characters, as produced
by the vis(3) function, back into
its 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.
.LP
.I Strunvis
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).
.LP
.I Unvis
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
.I 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 an destination character.
.I Vis
has several return codes that must be handled properly.  They are:
.TP 
0 (zero)
Another character is necessary; nothing has been recognized yet.
.TP
UNVIS_VALID     
A valid character has been recognized and is available at the location
pointed to by cp.
.TP
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.
.TP
UNVIS_NOCHAR
A valid sequence was detected, but no character was produced.  This
return code is necessary to indicate a logical break between characters.
.TP
UNVIS_SYNBAD
An invalid esacpe sequence was detected, or the decoder is in an
unknown state.  The decoder is placed into the starting state.
.LP
When all bytes in the stream have been processed, call
.I unvis
one more time with flag set to
.B UNVIS_END
to extract any remaining character (the character passed in is ignored).
.LP
The following code fragment illustrates a proper use of
.IR unvis .
.PP
.nf
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);
.fi
.SH "SEE ALSO"
vis(1)