VIS(3) | Library Functions Manual | VIS(3) |
vis
, nvis
,
strvis
, stravis
,
strnvis
, strvisx
,
strnvisx
, strenvisx
,
svis
, snvis
,
strsvis
, strsnvis
,
strsvisx
, strsnvisx
,
strsenvisx
— visually encode
characters
Standard C Library (libc, -lc)
#include
<vis.h>
char *
vis
(char
*dst, int c,
int flag,
int nextc);
char *
nvis
(char
*dst, size_t dlen,
int c,
int flag,
int nextc);
int
strvis
(char
*dst, const char
*src, int
flag);
int
stravis
(char
**dst, const char
*src, int
flag);
int
strnvis
(char
*dst, size_t dlen,
const char *src,
int flag);
int
strvisx
(char
*dst, const char
*src, size_t len,
int flag);
int
strnvisx
(char
*dst, size_t dlen,
const char *src,
size_t len,
int flag);
int
strenvisx
(char
*dst, size_t dlen,
const char *src,
size_t len,
int flag,
int *cerr_ptr);
char *
svis
(char
*dst, int c,
int flag,
int nextc,
const char *extra);
char *
snvis
(char
*dst, size_t dlen,
int c,
int flag,
int nextc,
const char *extra);
int
strsvis
(char
*dst, const char
*src, int flag,
const char *extra);
int
strsnvis
(char
*dst, size_t dlen,
const char *src,
int flag,
const char *extra);
int
strsvisx
(char
*dst, const char
*src, size_t len,
int flag,
const char *extra);
int
strsnvisx
(char
*dst, size_t dlen,
const char *src,
size_t len,
int flag,
const char *extra);
int
strsenvisx
(char
*dst, size_t dlen,
const char *src,
size_t len,
int flag,
const char *extra,
int *cerr_ptr);
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 null terminated, and a
pointer to the end of the string is returned. The maximum length of any
encoding is four bytes (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 bytes
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
(),
stravis
(),
strnvis
(),
strvisx
(),
and
strnvisx
()
functions copy into dst a visual representation of the
string src. The strvis
() and
strnvis
() functions encode characters from
src up to the first NUL
. The
strvisx
() and strnvisx
()
functions encode exactly len characters from
src (this is useful for encoding a block of data that
may contain NUL
's). Both forms
NUL
terminate dst. The size of
dst must be four times the number of bytes encoded
from src (plus one for the
NUL
). Both forms return the number of characters in
dst (not including the trailing
NUL
). The stravis
() function
allocates space dynamically to hold the string. The
“n
” versions of the functions also
take an additional argument dlen that indicates the
length of the dst buffer. If
dlen is not large enough to fit the converted string
then the strnvis
() and
strnvisx
() functions return -1 and set
errno to ENOSPC
. The
strenvisx
()
function takes an additional argument, cerr_ptr, that
is used to pass in and out a multibyte conversion error flag. This is useful
when processing single characters at a time when it is possible that the
locale may be set to something other than the locale of the characters in
the input data.
The functions
svis
(),
snvis
(),
strsvis
(),
strsnvis
(),
strsvisx
(),
strsnvisx
(),
and
strsenvisx
()
correspond to vis
(), nvis
(),
strvis
(), strnvis
(),
strvisx
(), strnvisx
(), and
strenvisx
() but have an additional argument
extra, pointing to a NUL
terminated list of characters. These characters will be copied encoded or
backslash-escaped into dst. These functions are useful
e.g. to remove the special meaning of certain characters to shells.
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), strunvis(3) or strnunvis(3) functions.
There are two parameters that can be controlled: the
range of characters that are encoded (applies only to
vis
(),
nvis
(),
strvis
(), strnvis
(),
strvisx
(), and strnvisx
()),
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_DQ
VIS_GLOB
*
’,
‘?
’,
‘[
’, and
‘#
’) recognized by
glob(3).VIS_SHELL
'
’,
‘`
’,
‘"
’,
‘;
’,
‘&
’,
‘<
’,
‘>
’,
‘(
’,
‘)
’,
‘|
’,
‘]
’,
‘\
’,
‘$
’,
‘!
’,
‘^
’, and
‘~
’).VIS_SP
VIS_TAB
VIS_NL
VIS_WHITE
VIS_SP
|
VIS_TAB
|
VIS_NL
.VIS_META
VIS_WHITE
|
VIS_GLOB
|
VIS_SHELL
.VIS_SAFE
(The above flags have no effect for
svis
(),
snvis
(),
strsvis
(),
strsnvis
(),
strsvisx
(),
and
strsnvisx
().
When using these functions, place all graphic characters to be encoded in an
array pointed to by extra. In general, the backslash
character should be included in this array, see the warning on the use of
the VIS_NOSLASH
flag below).
There are six forms of encoding. All forms use the backslash
character ‘\
’ to introduce a special
sequence; two backslashes are used to represent a real backslash, except
VIS_HTTPSTYLE
that uses
‘%
’, or
VIS_MIMESTYLE
that uses
‘=
’. These are the visual formats:
M
’ to represent meta
characters (characters with the 8th bit set), and use caret
‘^
’ to represent control characters
(see iscntrl(3)). The following
formats are used:
\^C
C
’. Spans characters
‘\000
’ through
‘\037
’, and
‘\177
’ (as
‘\^?
’).\M-C
C
’ with
the 8th bit set. Spans characters
‘\241
’ through
‘\376
’.\M^C
C
’
with the 8th bit set. Spans characters
‘\200
’ through
‘\237
’, and
‘\377
’ (as
‘\M^?
’).\040
\240
VIS_CSTYLE
\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.
Non-printable characters without C-style backslash sequences use the default representation.
VIS_OCTAL
\ddd
’ where
d represents
an octal digit.VIS_CSTYLE
|
VIS_OCTAL
VIS_CSTYLE
except that non-printable
characters without C-style backslash sequences use a three digit octal
sequence.VIS_HTTPSTYLE
%xx
’ where
x represents a
lower case hexadecimal digit.VIS_MIMESTYLE
=XX
’ where
X represents
an upper case hexadecimal 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.
These functions support multibyte character input. The encoding
conversion is influenced by the setting of the
LC_CTYPE
environment variable which defines the set
of characters that can be copied without encoding.
If VIS_NOLOCALE
is set, processing is done
assuming the C locale and overriding any other environment settings.
When 8-bit data is present in the input,
LC_CTYPE
must be set to the correct locale or to the
C locale. If the locales of the data and the conversion are mismatched,
multibyte character recognition may fail and encoding will be performed
byte-by-byte instead.
As noted above, dst must be four times the
number of bytes processed from src. But note that each
multibyte character can be up to MB_LEN_MAX
bytes so
in terms of multibyte characters, dst must be four
times MB_LEN_MAX
times the number of characters
processed from src.
LC_CTYPE
The functions nvis
() and
snvis
() will return NULL
and
the functions strnvis
(),
strnvisx
(), strsnvis
(), and
strsnvisx
(), will return -1 when the
dlen destination buffer size is not enough to perform
the conversion while setting errno to:
ENOSPC
]unvis(1), vis(1), glob(3), unvis(3)
T. Berners-Lee, Uniform Resource Locators (URL), RFC 1738.
Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies, RFC 2045.
The vis
(),
strvis
(), and strvisx
()
functions first appeared in 4.4BSD. The
svis
(), strsvis
(),
strsvisx
() nvis
(),
strnvis
(), strnvisx
(),
snvis
(), strsnvis
() and
strsnvisx
() functions as well as multibyte character
support were added in OS X 10.12.
April 22, 2017 | macOS 14.6 |