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VIS(3)		       FreeBSD Library Functions Manual			VIS(3)

NAME
     vis, nvis,	strvis,	strnvis, strvisx, strnvisx, strenvisx, svis, snvis,
     strsvis, strsnvis,	strsvisx, strsnvisx, strsenvisx	-- visually encode
     characters

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <vis.h>

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

     char *
     nvis(char *dst, size_t dlen, int c, int flag, int nextc);

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

     int
     strnvis(char *dst,	size_t dlen, const char	*src, int flag);

     int
     strvisx(char *dst,	const char *src, size_t	len, int flag);

     int
     strnvisx(char *dst, size_t	dlen, const char *src, size_t len, int flag);

     int
     strenvisx(char *dst, size_t dlen, const char *src,	size_t len, int	flag,
	 int *cerr_ptr);

     char *
     svis(char *dst, int c, int	flag, int nextc, const char *extra);

     char *
     snvis(char	*dst, size_t dlen, int c, int flag, int	nextc,
	 const char *extra);

     int
     strsvis(char *dst,	const char *src, int flag, const char *extra);

     int
     strsnvis(char *dst, size_t	dlen, const char *src, int flag,
	 const char *extra);

     int
     strsvisx(char *dst, const char *src, size_t len, int flag,
	 const char *extra);

     int
     strsnvisx(char *dst, size_t dlen, const char *src,	size_t len, int	flag,
	 const char *extra);

     int
     strsenvisx(char *dst, size_t dlen,	const char *src, size_t	len, int flag,
	 const char *extra, int	*cerr_ptr);

DESCRIPTION
     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 bytes (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 bytes 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(), strnvis(), strvisx(), and strnvisx()	functions copy into
     dst a visual representation of the	string src.  The strvis() and
     strnvis() functions encode	characters from	src up to the first NUL.  The
     strvisx() and strnvisx() functions	encode 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 bytes encoded from src (plus one	for the	NUL).  Both forms
     return the	number of characters in	dst (not including the trailing	NUL).
     The ``n'' versions	of the functions also take an additional argument dlen
     that indicates the	length of the dst buffer.  If dlen is not large	enough
     to	fit the	converted string then the strnvis() and	strnvisx() functions
     return -1 and set errno to	ENOSPC.	 The strenvisx() function takes	an
     additional	argument, cerr_ptr, that is used to pass in and	out a multi-
     byte conversion error flag.  This is useful when processing single	char-
     acters at a time when it is possible that the locale may be set to	some-
     thing other than the locale of the	characters in the input	data.

     The functions svis(), snvis(), strsvis(), strsnvis(), strsvisx(),
     strsnvisx(), and strsenvisx() correspond to vis(),	nvis(),	strvis(),
     strnvis(),	strvisx(), strnvisx(), and strenvisx() but have	an additional
     argument extra, pointing to a NUL terminated list of characters.  These
     characters	will be	copied encoded or backslash-escaped into dst.  These
     functions are useful e.g. to remove the special meaning of	certain	char-
     acters to shells.

     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), strunvis(3) or strnunvis(3) functions.

     There are two parameters that can be controlled: the range	of characters
     that are encoded (applies only to vis(), nvis(), strvis(),	strnvis(),
     strvisx(),	and strnvisx()), 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 the magic characters (`*',	`?', `[' and `#') rec-
		 ognized 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	unex-
		 pected	functions.  Currently this form	allows space, tab,
		 newline, backspace, bell, and return -- in addition to	all
		 graphic characters -- unencoded.

     (The above	flags have no effect for svis(), snvis(), strsvis(),
     strsnvis(), strsvisx(), and strsnvisx().  When using these	functions,
     place all graphic characters to be	encoded	in an array pointed to by
     extra.  In	general, the backslash character should	be included in this
     array, see	the warning on the use of the VIS_NOSLASH flag below).

     There are four forms of encoding.	All forms use the backslash character
     `\' to introduce a	special	sequence; two backslashes are used to repre-
     sent a real backslash, except VIS_HTTPSTYLE that uses `%',	or
     VIS_MIMESTYLE that	uses `='.  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 charac-
		 ters (see iscntrl(3)).	 The following formats are used:

		 \^C	Represents the control character `C'.  Spans charac-
			ters `\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 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 represen-
		 tation	is used	to avoid ambiguity.

     VIS_OCTAL	 Use a three digit octal sequence.  The	form is	`\ddd' where d
		 represents an octal digit.

     VIS_HTTPSTYLE
		 Use URI encoding as described in RFC 1738.  The form is `%xx'
		 where x represents a lower case hexadecimal digit.

     VIS_MIMESTYLE
		 Use MIME Quoted-Printable encoding as described in RFC	2045,
		 only don't break lines	and don't handle CRLF.	The form is
		 `=XX' where X represents an upper case	hexadecimal 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.

MULTIBYTE CHARACTER SUPPORT
     These functions support multibyte character input.	 The encoding conver-
     sion is influenced	by the setting of the LC_CTYPE environment variable
     which defines the set of characters that can be copied without encoding.

     When 8-bit	data is	present	in the input, LC_CTYPE must be set to the cor-
     rect locale or to the C locale.  If the locales of	the data and the con-
     version are mismatched, multibyte character recognition may fail and
     encoding will be performed	byte-by-byte instead.

     As	noted above, dst must be four times the	number of bytes	processed from
     src.  But note that each multibyte	character can be up to MB_LEN_MAX
     bytes so in terms of multibyte characters,	dst must be four times
     MB_LEN_MAX	times the number of characters processed from src.

ENVIRONMENT
     LC_CTYPE  Specify the locale of the input data.  Set to C if the input
	       data locale is unknown.

ERRORS
     The functions nvis() and snvis() will return NULL and the functions
     strnvis(),	strnvisx(), strsnvis(),	and strsnvisx(), will return -1	when
     the dlen destination buffer size is not enough to perform the conversion
     while setting errno to:

     [ENOSPC]  The destination buffer size is not large	enough to perform the
	       conversion.

SEE ALSO
     unvis(1), vis(1), glob(3),	unvis(3)

     T.	Berners-Lee, Uniform Resource Locators (URL), RFC 1738.

     Multipurpose Internet Mail	Extensions (MIME) Part One: Format of Internet
     Message Bodies, RFC 2045.

HISTORY
     The vis(),	strvis(), and strvisx()	functions first	appeared in 4.4BSD.
     The svis(), strsvis(), and	strsvisx() functions appeared in NetBSD	1.5
     and FreeBSD 9.2.  The buffer size limited versions	of the functions
     (nvis(), strnvis(), strnvisx(), snvis(), strsnvis(), and strsnvisx())
     appeared in and FreeBSD 9.2.  Myltibyte character support was added in
     NetBSD 7.0	and FreeBSD 9.2.

FreeBSD	9.3		       February	19, 2013		   FreeBSD 9.3

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | MULTIBYTE CHARACTER SUPPORT | ENVIRONMENT | ERRORS | SEE ALSO | HISTORY

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