In stdlib.h
In vis.h
Ft char *
Fn vis char *dst int c int flag int nextc
Ft int
Fn strvis char *dst const char *src int flag
Ft int
Fn strnvis char *dst const char *src size_t size int flag
Ft int
Fn strvisx char *dst const char *src size_t len int flag
DESCRIPTION
The
Fn 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 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
Fa flag
parameter 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
Fn strvis ,
Fn strnvis
and
Fn strvisx
functions copy into
Fa dst
a visual representation of
the string
Fa src .
The
Fn strvis
function encodes characters from
Fa src
up to the first NUL.
The
Fn strnvis
function encodes characters from
Fa src
up to the first NUL or the end of
Fa dst ,
as indicated by
Fa size .
The
Fn strvisx
function encodes exactly
Fa len
characters from
Fa src
(this
is useful for encoding a block of data that may contain NULs).
All three forms NUL terminate
Fa dst ,
except for
Fn strnvis
when
Fa size
is zero, in which case
Fa dst
is not touched.
For
Fn strvis
and
Fn strvisx ,
the size of
Fa dst
must be four times the number
of characters encoded from
Fa src
(plus one for the NUL).
Fn strvis
and
Fn strvisx
return the number of characters in
Fa dst
(not including the trailing NUL).
Fn strnvis
returns the length that
Fa 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
Fn strnvis
must not be used without checking it against
Fa 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:
When using this format, the
Fa nextc
parameter 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_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.