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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
     character 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
     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
     characters 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 `#')
                 recognized 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
                 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 four forms of encoding.  All forms use the backslash character
     `\' to introduce a special sequence; two backslashes are used to
     represent 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
                 characters (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
                        `\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
                 representation 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
     conversion 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
     correct locale or to the C locale.  If the locales of the data and the
     conversion 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 11.0-PRERELEASE        February 19, 2013       FreeBSD 11.0-PRERELEASE

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

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