VIS(3)VIS(3)NAMEvis - visually encode characters
SYNOPSIS
#include <vis.h>
char *vis(dst, c, flag, nextc)
char *dst, c, nextc;
int flag;
int strvis(dst, src, flag)
char *dst, *src;
int flag;
int strvisx(dst, src, len, flag)
char *dst, *src;
int len, flag;
DESCRIPTION
Vis copies into dst a string which represents the character c. If c
needs no encoding, it is copied in unaltered. The string is null ter‐
minated, and a pointer to the end of the string is returned. The maxi‐
mum length of any encoding is four characters (not including the trail‐
ing NULL); thus, when encoding a set of characters into a buffer, the
size of the buffer should be four times the number of characters
encoded, plus one for the trailing NULL. The flag parameter is used
for altering the default range of characters considered for encoding
and for altering the visual representation. The additional character,
nextc, is only used when selecting the VIS_CSTYLE encoding format
(explained below).
Strvis and strvisx copy into dst a visual representation of the string
src. Strvis encodes characters from src up to the first NULL. Strvisx
encodes exactly len characters from src (this is useful for encoding a
block of data that may contain NULL's). Both forms NULL terminate dst.
Dst must be four times the number of characters encoded from src (plus
one for the NULL). Both forms return the number of characters in dst
(not including the trailing NULL).
The encoding is a unique, invertible representation comprised entirely
of graphic characters; it can be decoded back into the original form
using the unvis(3) or strunvis(3) functions.
There are two parameters that can be controlled: the range of charac‐
ters that are encoded, and the type of representation used. By
default, all non-graphic characters (see isgraph(3)) except space, tab,
and newline are encoded. The following flags alter this:
VIS_SP Also encode space.
VIS_TAB
Also encode tab.
VIS_NL Also encode newline.
VIS_WHITE
Synonym for VIS_SP | VIS_TAB | VIS_NL.
VIS_SAFE
Only encode "unsafe" characters. Unsafe means control charac‐
ters which may cause common terminals to perform unexpected
functions. Currently this form allows space, tab, newline,
backspace, bell, and return - in addition to all graphic charac‐
ters - unencoded.
There are three forms of encoding. All forms use the backslash charac‐
ter (``\'') to introduce a special sequence; two backslashes are used
to represent a real backslash. These are the visual formats:
(default)
Use an ``M'' to represent meta characters (characters with the
8th bit set), and use carat (``^'') to represent control charac‐
ters see (iscntrl(3)). The following formats are used:
\^C Represents the control character ``C''. Spans characters
\000 through \037, and \177 (as \^?).
\M-C Represents character ``C'' with the 8th bit set. Spans
characters \241 through \376.
\M^C Represents control character ``C'' with the 8th bit set.
Spans characters \200 through \237, and \377 (as \M^?).
\040 Represents ACSII space.
\240 Represents Meta-space.
VIS_CSTYLE
Use C-style backslash sequences to represent standard non-print‐
able characters. The following sequences are used to represent
the indicated characters:
\a - BEL (007)
\b - BS (010)
\f - NP (014)
\n - NL (012)
\r - CR (015)
\t - HT (011)
\v - VT (013)
\0 - NUL (000)
When using this format, the nextc parameter is looked at to
determine if a NULL character can be encoded as ``\0'' instead
of ``\000''. If nextc is an octal digit, the latter representa‐
tion is used to avoid ambiguity.
VIS_OCTAL
Use a three digit octal sequence. The form is ``\ddd'' where d
represents an octal digit.
There is one additional flag, VIS_NOSLASH, which inhibits the doubling
of backslashes and the backslash before the default format (that is,
control characters are represented by ^C and meta characters as M-C).
With this flag set, the encoding is ambiguous and non-invertible.
SEE ALSOvis(1), unvis(1), unvis(3)4.4 Berkeley Distribution June 23, 1990 VIS(3)