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

     vis, nvis,	strvis,	stravis, strnvis, strvisx, strnvisx, strenvisx,	svis,
     snvis, strsvis, strsnvis, strsvisx, strsnvisx, strsenvisx -- visually en-
     code characters

     Standard C	Library	(libc, -lc)

     #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);

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

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

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

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

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

     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);

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

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

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

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

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

     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 se-
     lecting the VIS_CSTYLE encoding format (explained below).

     The strvis(), stravis(), 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 re-
     turn the number of	characters in dst (not including the trailing NUL).
     The stravis() function allocates space dynamically	to hold	the string.
     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 ad-
     ditional argument,	cerr_ptr, that is used to pass in and out a multibyte
     conversion	error flag.  This is useful when processing single characters
     at	a time when it is possible that	the locale may be set to something
     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 de-
     fault, all	non-graphic characters,	except space, tab, and newline are en-
     coded (see	isgraph(3)).  The following flags alter	this:

     VIS_DQ	 Also encode double quotes

     VIS_GLOB	 Also encode the magic characters (`*',	`?', `[', and `#')
		 recognized by glob(3).

     VIS_SHELL	 Also encode the meta characters used by shells	(in addition
		 to the	glob characters): (`'',	``', `"', `;', `&', `<', `>',
		 `(', `)', `|',	`]', `\', `$', `!', `^', 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.  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.

     (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 six 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

		 \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.

		 Non-printable characters without C-style backslash sequences
		 use the default representation.

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

		 Same as VIS_CSTYLE except that	non-printable characters with-
		 out C-style backslash sequences use a three digit octal se-

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

		 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.

     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.

     If	VIS_NOLOCALE is	set, processing	is done	assuming the C locale and
     overriding	any other environment settings.

     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 en-
     coding 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.

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

     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

     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.

     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()) ap-
     peared in NetBSD 6.0 and FreeBSD 9.2.  Multibyte character	support	was
     added in NetBSD 7.0 and FreeBSD 9.2.

BSD				April 22, 2017				   BSD


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