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NAME    [Toc]    [Back]

     vis, strvis, strnvis, strvisx - visually encode characters

SYNOPSIS    [Toc]    [Back]

     #include <stdlib.h>
     #include <vis.h>

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

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

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

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

DESCRIPTION    [Toc]    [Back]

     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 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() and strvisx()  functions  copy  into
dst a visual
     representation of the string src.  The strvis() function encodes characters
 from src up to the first NUL.  The  strnvis()  function
encodes characters
  from  src  up to the first NUL or the end of dst, as
indicated by
     size.  The strvisx() function encodes exactly len characters
from src
     (this  is  useful for encoding a block of data that may contain NULs).  All
     three forms NUL terminate dst,  except  for  strnvis()  when
size is zero, in
     which  case dst is not touched.  For strvis() and strvisx(),
the size of
     dst must be four times the number of characters encoded from
src (plus
     one  for the NUL).  strvis() and strvisx() return the number
of characters
     in dst (not including the trailing NUL).  strnvis()  returns
the length
     that  dst would become if it were of unlimited size (similar
     snprintf(3) or strlcpy(3)).  This  can  be  used  to  detect
truncation but it
     also  means  that  the return value of strnvis() must not be
used without
     checking it against size.

     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) 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.  These are
control characters
 which may cause common terminals to perform
                 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 a caret `^'  to  represent
control characters
  (see iscntrl(3)).  The following formats
are used:

                 C     Represents  the  control  character   `C'.
Spans characters
  ` 00'  through ` 37', 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

                  40   Represents ASCII space.

                 240   Represents Meta-space.

     VIS_CSTYLE   Use  C-style  backslash  sequences to represent
standard nonprintable
 characters.  The  following  sequences
are used to
                 represent the indicated characters:

                        - BEL (007)
                       -BS (010)
                       - NP (014)

                       - SP (040)
                        - HT (011)
                       - VT (013)
                         - NUL (000)

                 When  using  this format, the nextc parameter is
looked at to
                 determine if a NUL character can be  encoded  as
` ' instead
                 of  ` 00'.  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
`dd' 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    [Toc]    [Back]

     unvis(1), vis(1), snprintf(3), strlcpy(3), unvis(3)

HISTORY    [Toc]    [Back]

     The  vis(),  strvis() and strvisx() functions first appeared
in 4.4BSD.
     The strnvis() function first appeared in OpenBSD 2.9.

OpenBSD      3.6                           June      9,      1993
[ Back ]
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