4.4BSD/usr/share/man/cat3/unvis.0

UNVIS(3)                    BSD Programmer's Manual                   UNVIS(3)

NNAAMMEE
     uunnvviiss, ssttrruunnvviiss - decode a visual representation of characters

SSYYNNOOPPSSIISS
     ##iinncclluuddee <<vviiss..hh>>

     _i_n_t
     uunnvviiss(_u___c_h_a_r _*_c_p, _u___c_h_a_r _c, _i_n_t _*_a_s_t_a_t_e, _i_n_t _f_l_a_g);

     _i_n_t
     ssttrruunnvviiss(_c_h_a_r _*_d_s_t, _c_h_a_r _*_s_r_c);

DDEESSCCRRIIPPTTIIOONN
     The uunnvviiss() and ssttrruunnvviiss() functions are used to decode a visual repre-
     sentation of characters, as produced by the vis(3) function, back into
     the original form.  Unvis 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 _c_p. Strunvis decodes the charac-
     ters pointed to by _s_r_c into the buffer pointed to by _d_s_t.

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

     The uunnvviiss() function implements a state machine that can be used to de-
     code an arbitrary stream of bytes.  All state associated with the bytes
     being decoded is stored outside the uunnvviiss() 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 uunnvviiss() with each successive byte, along with a
     pointer to this integer, and a pointer to an destination character.  The
     unvis function has several return codes that must be handled properly.
     They are:

     0 (zero)         Another character is necessary; nothing has been recog-
                      nized 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 pro-
                      duced.  This return code is necessary to indicate a log-
                      ical break between characters.

     UNVIS_SYNBAD     An invalid esacpe 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 uunnvviiss() 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 uunnvviiss().

           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);

SSEEEE AALLSSOO
     vis(1)

HHIISSTTOORRYY
     The uunnvviiss function first appeared in 4.4BSD.

4.4BSD                           June 9, 1993                                2