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VIS(3)			 BSD Library Functions Manual			VIS(3)

     vis -- visually encode characters

     Standard C	Library	(libc, -lc)

     #include <vis.h>

     char *
     vis(char *dst, int	c, int flag, int nextc);

     strvis(char *dst, const char *src,	int flag);

     strvisx(char *dst,	const char *src, size_t	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 argument 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
     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 characters encoded from 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 `#') recog-
		 nized 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	char-
		 acters	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 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 caret `^'	to represent control
		    characters see (iscntrl(3)).  The following	formats	are

		    \^C	   Represents the control character `C'.  Spans	char-
			   acters `\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 argument is looked at to
		    determine if a NUL character can be	encoded	as `\0'	in-
		    stead of `\000'.  If 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.

     unvis(1), unvis(3)

     R.	Fielding, Relative Uniform Resource Locators, RFC1808.

     These functions first appeared in 4.4BSD.

     The vis family of functions do not	recognize multibyte characters,	and
     thus may consider them to be non-printable	when they are in fact print-
     able (and vice versa.)

BSD				 April 9, 2006				   BSD


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