NAME
vis,
nvis,
strvis,
stravis,
strnvis,
strvisx,
strnvisx,
strenvisx,
svis,
snvis,
strsvis,
strsnvis,
strsvisx,
strsnvisx,
strsenvisx —
visually encode
characters
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#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);
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 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
- Also encode double quotes
-
-
VIS_GLOB
- Also encode the magic characters
(‘
*
’,
‘?
’,
‘[
’, and
‘#
’) recognized by
glob(3).
-
-
VIS_SHELL
- Also encode the meta characters used by shells (in addition
to the glob characters): (‘
'
’,
‘`
’,
‘"
’,
‘;
’,
‘&
’,
‘<
’,
‘>
’,
‘(
’,
‘)
’,
‘|
’,
‘]
’,
‘\
’,
‘$
’,
‘!
’,
‘^
’, 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_META
- Synonym for
VIS_WHITE
|
VIS_GLOB
| VIS_SHELL
.
-
-
VIS_SAFE
- Only encode “unsafe” characters. Unsafe means
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.
(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 four 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:
-
-
- (default)
- Use an ‘
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
- 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.
-
-
VIS_HTTPSTYLE
- Use URI encoding as described in RFC 1738. The form is
‘
%xx
’ where x
represents a lower case hexadecimal digit.
-
-
VIS_MIMESTYLE
- Use MIME Quoted-Printable encoding as described in RFC
2045, only don't break lines and don't handle CRLF. The form is
‘
=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.
MULTIBYTE CHARACTER SUPPORT
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.
ENVIRONMENT
-
-
LC_CTYPE
- Specify the locale of the input data. Set to C if the input
data locale is unknown.
ERRORS
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
]
- The destination buffer size is not large enough to perform
the conversion.
SEE ALSO
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.
HISTORY
The
vis(),
strvis(), and
strvisx() functions first appeared in
4.4BSD. The
svis(),
strsvis(), and
strsvisx() functions
appeared in
NetBSD 1.5. The buffer size limited
versions of the functions (
nvis(),
strnvis(),
strnvisx(),
snvis(),
strsnvis(), and
strsnvisx()) appeared in
NetBSD 6.0
and
FreeBSD 9.2. Multibyte character support was added
in
NetBSD 7.0 and
FreeBSD
9.2.