NAME

       unvis, strunvis, strnunvis — decode a visual representation of characters

LIBRARY

       library “libbsd”

SYNOPSIS

       #include <bsd/vis.h>

       int
       unvis(char *cp, char c, int *astate, int flag);

       int
       strunvis(char *dst, char *src);

       ssize_t
       strnunvis(char *dst, char *src, size_t size);

DESCRIPTION

       The  unvis(),  strunvis()  and  strnunvis()  functions  are  used  to  decode  a visual representation 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 cp.

       strunvis() decodes the characters pointed to by src into the buffer pointed to by dst.

       strnunvis() decodes the characters pointed to by src into the buffer pointed to by dst, writing a maximum
       of size bytes.  The strunvis() 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).  strunvis() terminates the destination string with a trailing NUL byte; strnunvis() does so if
       size is larger than 0.

       The unvis() 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() 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() with each successive
       byte, along with a pointer to this integer, and a pointer to a destination character.

RETURN VALUES

       The unvis() 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() one more time with flag set to UNVIS_END
       to extract any remaining character (the character passed in is ignored).

       The strunvis() function returns the number of bytes written (not counting the trailing NUL byte) or -1 if
       an error occurred.

       The strnunvis() function returns the number of bytes (not counting the trailing NUL byte) that  would  be
       needed to fully convert the input string, or -1 if an error occurred.

EXAMPLES

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

             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!\n");
                             exit(1);
                     }
             }
             if (unvis(&out, (char)0, &state, UNVIS_END) == UNVIS_VALID)
                     (void) putchar(out);

SEE ALSO

       unvis(1), vis(1), vis(3)

HISTORY

       The unvis() function first appeared in 4.4BSD.

Debian                                            May 31, 2007                                          UNVIS(3)