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VIS(3) |
FreeBSD 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
- 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 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:
- (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.
Non-printable characters without C-style backslash sequences
use the default representation.
VIS_OCTAL
- Use a three digit octal sequence. The form is
‘
\ddd ’ where d
represents an octal digit.
VIS_CSTYLE
| VIS_OCTAL
- Same as
VIS_CSTYLE except that non-printable
characters without C-style backslash sequences use a three digit octal
sequence.
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.
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
- Specify the locale of the input data. Set to C if the input data locale is
unknown.
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.
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 (), and strsvisx ()
functions appeared in NetBSD 1.5 and
FreeBSD 9.2. 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.
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