VIS(3) BSD Library Functions Manual VIS(3)
NAME
vis, strvis, strnvis, strvisx -- visually encode characters
LIBRARY
Utility functions from BSD systems (libbsd, -lbsd)
SYNOPSIS
#include <stdlib.h>
#include <bsd/vis.h>
char *
vis(char *dst, int c, int flag, int nextc);
int
strvis(char *dst, const char *src, int flag);
int
strnvis(char *dst, const char *src, size_t size, int flag);
int
strvisx(char *dst, const char *src, size_t len, int flag);
DESCRIPTION
The vis() function copies into dst a string which represents the character c. If c needs no encoding, it is copied in unaltered. The string
is NUL terminated and a pointer to the end of the string is returned. The maximum length of any encoding is four characters (not including
the trailing NUL); thus, when encoding a set of characters into a buffer, the size of the buffer should be four times the number of charac-
ters encoded, plus one for the trailing NUL. 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).
The strvis(), strnvis() and strvisx() functions copy into dst a visual representation of the string src. The strvis() function encodes char-
acters from src up to the first NUL. The strnvis() function encodes characters from src up to the first NUL or the end of dst, as indicated
by size. The strvisx() function encodes exactly len characters from src (this is useful for encoding a block of data that may contain NULs).
All three forms NUL terminate dst, except for strnvis() when size is zero, in which case dst is not touched. For strvis() and strvisx(), the
size of dst must be four times the number of characters encoded from src (plus one for the NUL). strvis() and strvisx() return the number of
characters in dst (not including the trailing NUL). strnvis() returns the length that dst would become if it were of unlimited size (similar
to snprintf(3) or strlcpy(3)). This can be used to detect truncation but it also means that the return value of strnvis() must not be used
without checking it against size.
The encoding is a unique, invertible representation composed 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 characters that are encoded, and the type of representation used. By default,
all non-graphic characters except space, tab, and newline are encoded (see isgraph(3)). The following flags alter this:
VIS_GLOB Also encode magic characters recognized by glob(3) ('*', '?', '[') and '#'.
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. These are control characters which may cause common terminals to perform unexpected func-
tions. Currently this form allows space, tab, newline, backspace, bell, and return -- in addition to all graphic characters --
unencoded.
There are three forms of encoding. All forms use the backslash '' character 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 a caret '^' to represent control characters
(see iscntrl(3)). The following formats are used:
^C Represents the control character 'C'. Spans characters '