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VIS(3) OpenBSD Programmer's Manual VIS(3)
vis, strvis, strvisx - visually encode characters
vis(char *dst, char c, int flag, char nextc);
strvis(char *dst, char *src, int flag);
strvisx(char *dst, char *src, int len, int flag);
The vis() function copies into dst a string which represents the charac-
ter 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 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 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() and strvisx() functions copy into dst a visual representa-
tion of the string src. The strvis() function encodes characters from src
up to the first NUL. The strvisx() function encodes exactly len charac-
ters from src (this is useful for encoding a block of data that may con-
tain NULs). Both forms null terminate dst. The size of dst must be four
times the number of characters encoded from src (plus one for the NUL).
Both forms return the number of characters in dst (not including the
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_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 charac-
ters 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 `\' char-
acter to introduce a special sequence; two backslashes are used to repre-
sent 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 char-
acters (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
\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)
\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 representa-
tion 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.
unvis(1), vis(1), unvis(3)
These functions first appeared in 4.4BSD.
OpenBSD 2.6 June 9, 1993 2
Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.
(Corrections, notes, and links courtesy of RocketAware.com)
FreeBSD Sources for vis(3) functions
OpenBSD sources for vis(3)
Up to: NUL Terminated String processing - NUL terminated string operations (strcpy, strlen, etc)
Up to: Character Tests and Operations - isblank, toupper, etc.
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