#include <vis.h> char *
vis (char *dst int c int flag int nextc); int
strvis (char *dst const char *src int flag); int
strvisx (char *dst const char *src size_t len int flag);
DESCRIPTION
The
vis ();
function
copies into
Fa dst
a string which represents the character
Fa c .
If
Fa 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
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
Fa flag
argument is used for altering the default range of
characters considered for encoding and for altering the visual
representation.
The additional character,
Fa nextc ,
is only used when selecting the
VIS_CSTYLE
encoding format (explained below).
The
strvis ();
and
strvisx ();
functions copy into
Fa dst
a visual representation of
the string
Fa src .
The
strvis ();
function encodes characters from
Fa src
up to the
first
NUL
The
strvisx ();
function encodes exactly
Fa len
characters from
Fa src
(this
is useful for encoding a block of data that may contain
NUL 's
Both forms
NUL
terminate
Fa dst .
The size of
Fa dst
must be four times the number
of characters encoded from
Fa src
(plus one for the
NUL )
Both
forms return the number of characters in dst (not including
the trailing
NUL )
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
`('
* ,
`?'
,
`['
and
`#'
)
recognized by
glob(3).
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.
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.
There are four forms of encoding.
Most 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 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
Fa nextc
argument is looked at to determine
if a
NUL
character can be encoded as
`\0'
instead of
`\000'
If
Fa nextc
is an octal digit, the latter representation is used to
avoid ambiguity.
VIS_HTTPSTYLE
Use URI encoding as described in RFC 1808.
The form is
`%dd'
where
d
represents a hexadecimal digit.
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.
R. Fielding
Relative Uniform Resource Locators
RFC1808
HISTORY
These functions first appeared in
BSD 4.4
BUGS
The
family of functions do not recognize multibyte characters, and thus
may consider them to be non-printable when they are in fact printable
(and vice versa.)
