vis, strvis, strnvis, strvisx - visually encode characters
vis(char *dst, char c, int flag, char nextc);
strvis(char *dst, const char *src, int flag);
strnvis(char *dst, const char *src, size_t size, int flag);
strvisx(char *dst, const char *src, size_t len, int flag);
The vis() function copies into dst a string which represents
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
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 flag parameter is used
the default range of characters considered for encoding and
the visual representation. The additional character, nextc,
is only used
when selecting the VIS_CSTYLE encoding format (explained below).
The strvis(), strnvis() and strvisx() functions copy into
dst a visual
representation of the string src. The strvis() function encodes characters
from src up to the first NUL. The strnvis() function
from src up to the first NUL or the end of dst, as
size. The strvisx() function encodes exactly len characters
(this is useful for encoding a block of data that may contain NULs). All
three forms NUL terminate dst, except for strnvis() when
size is zero, in
which case dst is not touched. For strvis() and strvisx(),
the size of
dst must be four times the number of characters encoded from
one for the NUL). strvis() and strvisx() return the number
in dst (not including the trailing NUL). strnvis() returns
that dst would become if it were of unlimited size (similar
snprintf(3) or strlcpy(3)). This can be used to detect
truncation but it
also means that the return value of strnvis() must not be
checking it against size.
The encoding is a unique, invertible representation composed
graphic characters; it can be decoded back into the original
the unvis(3) or strunvis(3) functions.
There are two parameters that can be controlled: the range
that are encoded, and the type of representation used. By
non-graphic characters except space, tab, and newline are
isgraph(3)). The following flags alter this:
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
which may cause common terminals to perform
functions. Currently this form allows space,
backspace, bell, and return -- in addition to
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
(see iscntrl(3)). The following formats
C Represents the control character `C'.
` 00' through ` 37', and `177' (as
M-C Represents character `C' with the 8th bit
characters `241' through `376'.
M^C Represents control character `C' with the
8th bit set.
Spans characters `200' through `237', and
40 Represents ASCII space.
240 Represents Meta-space.
VIS_CSTYLE Use C-style backslash sequences to represent
characters. The following sequences
are used to
represent the indicated characters:
- BEL (007)
- NP (014)
- SP (040)
- HT (011)
- VT (013)
- NUL (000)
When using this format, the nextc parameter is
looked at to
determine if a NUL character can be encoded as
` ' instead
of ` 00'. 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
`dd' 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
this flag set, the encoding is ambiguous and non-invertible.
unvis(1), vis(1), snprintf(3), strlcpy(3), unvis(3)
The vis(), strvis() and strvisx() functions first appeared
The strnvis() function first appeared in OpenBSD 2.9.
OpenBSD 3.6 June 9, 1993
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