NAME¶
vis
,
strvis
,
strnvis
,
strvisx
—
visually encode characters
LIBRARY¶
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 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 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.
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
‘\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)
When using this format, the nextc parameter
is looked at to determine if a NUL character can be encoded as
‘\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.
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 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.