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VIS(3) | Library Functions Manual | VIS(3) |
NAME¶
vis, strvis, strnvis, strvisx — visually encode charactersLIBRARY¶
library “libbsd”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 characters 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 theVIS_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 characters 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 functions. Currently this form allows space, tab, newline, backspace, bell, and return -- in addition to all graphic characters -- unencoded.
\
’ 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 ‘\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 ASCII space.
\240
- Represents Meta-space.
VIS_CSTYLE
- Use C-style backslash sequences to represent standard
non-printable 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)\s
- SP (040)\t
- HT (011)\v
- VT (013)\0
- NUL (000)\0
’ instead of ‘\000
’. If nextc is an octal digit, the latter representation is used to avoid ambiguity. VIS_OCTAL
- Use a three digit octal sequence. The form is
‘
\ddd
’ where d represents an octal digit.
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 ALSO¶
unvis(1), vis(1), snprintf(3), strlcpy(3), unvis(3)HISTORY¶
The vis(), strvis() and strvisx() functions first appeared in 4.4BSD. The strnvis() function first appeared in OpenBSD 2.9.May 31, 2007 | Debian |