| VIS(3) | Library Functions Manual | VIS(3) | 
vis, nvis,
  strvis, stravis,
  strnvis, strvisx,
  strnvisx, strenvisx,
  svis, snvis,
  strsvis, strsnvis,
  strsvisx, strsnvisx,
  strsenvisx —
#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
  
  stravis(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);
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(),
    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 return 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 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_DQVIS_GLOB*’,
      ‘?’,
      ‘[’, and
      ‘#’) recognized by
      glob(3).VIS_SHELL'’,
      ‘`’,
      ‘"’,
      ‘;’,
      ‘&’,
      ‘<’,
      ‘>’,
      ‘(’,
      ‘)’,
      ‘|’,
      ‘]’,
      ‘\’,
      ‘$’,
      ‘!’,
      ‘^’, and
      ‘~’).VIS_SPVIS_TABVIS_NLVIS_WHITEVIS_SP |
      VIS_TAB
      |
      VIS_NL.VIS_METAVIS_WHITE |
      VIS_GLOB
      |
      VIS_SHELL.VIS_SAFE(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 represent a real backslash, except
    VIS_HTTPSTYLE that uses
    ‘%’, or
    VIS_MIMESTYLE that uses
    ‘=’. These are the visual formats:
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:
    \^CC’. Spans characters
          ‘\000’ through
          ‘\037’, and
          ‘\177’ (as
          ‘\^?’).\M-CC’ with
          the 8th bit set. Spans characters
          ‘\241’ through
          ‘\376’.\M^CC’
          with the 8th bit set. Spans characters
          ‘\200’ through
          ‘\237’, and
          ‘\377’ (as
          ‘\M^?’).\040\240VIS_CSTYLE\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.
Non-printable characters without C-style backslash sequences use the default representation.
VIS_OCTAL\ddd’ where d
      represents an octal digit.VIS_CSTYLE
    | VIS_OCTALVIS_CSTYLE except that non-printable
      characters without C-style backslash sequences use a three digit octal
      sequence.VIS_HTTPSTYLE%xx’ where x
      represents a lower case hexadecimal digit.VIS_MIMESTYLE=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.
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 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.
LC_CTYPEnvis() 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]T. Berners-Lee, Uniform Resource Locators (URL), RFC 1738.
Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies, RFC 2045.
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 and FreeBSD 9.2. Multibyte character
  support was added in NetBSD 7.0 and
  FreeBSD 9.2.
| April 22, 2017 | NetBSD 9.3 |