VIS(3)                    386BSD Programmer's Manual                    VIS(3)

NAME
     vis - visually encode characters

SYNOPSIS
     #include <vis.h>

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

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

     int
     strvisx(char *dst, char *src, int len, int flag)

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 characters (not
     including the trailing NULL); 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 NULL. 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() and strvisx() functions copy into dst a visual
     representation of the string src. The strvis() function encodes
     characters from src up to the first NULL. The strvisx() function encodes
     exactly len characters from src (this is useful for encoding a block of
     data that may contain NULL's). Both forms NULL terminate dst. The size of
     dst must be four times the number of characters encoded from src (plus
     one for the NULL). Both forms return the number of characters in dst (not
     including the trailing NULL).

     The encoding is a unique, invertible representation comprised 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_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.

     There are three forms of encoding.  All forms use the backslash character
     `\' to introduce a special sequence; two backslashes are used to

     represent a real backslash.  These are the visual formats:

     (default)   Use an `M' to represent meta characters (characters with the
                 8th bit set), and use carat `^' 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)
                       \t - HT (011)
                       \v - VT (013)
                       \0 - NUL (000)

                 When using this format, the nextc parameter is looked at to
                 determine if a NULL 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.

     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.

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

HISTORY
     These functions are currently under development.

BSD Experimental                April 19, 1991                               2