VIS(3)                  NetBSD Library Functions Manual                 VIS(3)

NAME
     vis, nvis, strvis, strnvis, strvisx, strnvisx, svis, snvis, strsvis,
     strsnvis, strsvisx strsnvisx -- 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);

     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);

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 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(), 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 characters 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 fix the converted string then the strnvis() and strnvisx() functions
     return -1 and set errno to ENOSPC.

     The functions svis(), snvis(), strsvis(), strsnvis(), strsvisx(), and
     strsnvisx() correspond to vis(), nvis(), strvis(), strnvis(), strvisx(),
     and strnvisx() 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_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 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.

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 length size is not enough to perform the con-
     version while setting errno to:

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

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

     T. Berners-Lee, Uniform Resource Locators (URL), RFC1738.

HISTORY
     The vis(), strvis(), and strvisx functions first appeared in 4.4BSD.  The
     svis(), strsvis(), and strsvisx() functions appeared in NetBSD 1.5.  The
     buffer size limited versions of the functions (nvis(), strnvis(),
     strnvisx(), snvis(), strsnvis(), and strsnvisx()) appeared in NetBSD 6.0.

NetBSD 6.0                      March 12, 2011                      NetBSD 6.0

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©1996-2014 Modified for NetBSD by Kimmo Suominen