unvis(3)                                                       unvis(3)

  unvis()

  NAME

    unvis(), strunvis() - decode a visual representation of characters

  SYNOPSIS

    #include 

    int unvis (char *cp, char c, int *astate, int flag)
    int strunvis (char *dst, char *src)

  DESCRIPTION

    The unvis(3) and strunvis(3) functions are used to decode a visual
    representation of characters, as produced by the vis(3) function, back
    into the original form. The unvis(3) function is called with successive
    characters in c until a valid sequence is recognized, at which time the
    decoded character is available at the character pointed to by cp. The
    strunvis(3) function decodes the characters pointed to by src into the
    buffer pointed to by dst.

    The strunvis(3) function simply copies src to dst, decoding any escape
    sequences along the way, and returns the number of characters placed into
    dst, or -1 if an invalid escape sequence was detected. The size of dst
    should be equal to the size of src (that is, no expansion takes place
    during decoding).

    The unvis(3) function implements a state machine that can be used to
    decode an arbitrary stream of bytes. All state associated with the bytes
    being decoded is stored outside the unvis(3) function (that is, a pointer
    to the state is passed in), so calls decoding different streams can be
    freely intermixed. To start decoding a stream of bytes, first initialize
    an integer to zero. Call unvis(3) with each successive byte, along with a
    pointer to this integer, and a pointer to a destination character. The
    unvis(3) function has several return codes that must be handled properly.
    They are:

    0 (zero)
        Another character is necessary; nothing has been recognized yet.

    UNVIS_VALID
        A valid character has been recognized and is available at the location
        pointed to by cp.

    UNVIS_VALIDPUSH
        A valid character has been recognized and is available at the location
        pointed to by cp; however, the character currently passed in should be
        passed in again.

    UNVIS_NOCHAR
        A valid sequence was detected, but no character was produced. This
        return code is necessary to indicate a logical break between
        characters.

    UNVIS_SYNBAD
        An invalid escape sequence was detected, or the decoder is in an
        unknown state. The decoder is placed into the starting state.

    When all bytes in the stream have been processed, call unvis(3) one more
    time with flag set to UNVIS_END to extract any remaining character (the
    character passed in is ignored).

    The following code fragment illustrates a proper use of unvis(3).

    int state = 0;
    char out;
    while ((ch = getchar()) != EOF) {
    again:
         switch(unvis(&out, ch, &state, 0)) {
         case 0:
         case UNVIS_NOCHAR:
              break;
         case UNVIS_VALID:
              (void) putchar(out);
              break;
         case UNVIS_VALIDPUSH:
              (void) putchar(out);
              goto again;
         case UNVIS_SYNBAD:
              (void)fprintf(stderr, "bad sequence!0);
         exit(1);
         }
    }
    if (unvis(&out, (char)0, &state, UNVIS_END) == UNVIS_VALID)
         (void) putchar(out);

  SEE ALSO

    vis(3)

    vis(1)

    unvis(1)

  USAGE NOTES

    All of these functions are thread safe.

    None of these functions are async-signal safe.