UNVIS(3)						   BSD Library Functions Manual 						  UNVIS(3)

NAME

     unvis, strunvis -- decode a visual representation of characters

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <vis.h>

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

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

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

DESCRIPTION

     The unvis(), strunvis() and strunvisx() functions are used to decode a visual representation of characters, as produced by the vis(3) func-
     tion, 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.

     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).

     The strunvisx() function does the same as the strunvis() function, but it allows you to add a flag that specifies the style the string src is
     encoded with.  Currently, the only supported flag is VIS_HTTPSTYLE.

     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.  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 flag argument is also used to specify the encoding style of the source.  If set to VIS_HTTPSTYLE, unvis() will decode URI strings as
     specified in RFC 1808.

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

SEE ALSO

     vis(1), vis(3)

     R. Fielding, Relative Uniform Resource Locators, RFC1808.

HISTORY

     The unvis() function first appeared in 4.4BSD.

BSD
								 December 11, 1993							       BSD