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.\" @(#)unvis.3 1.3 (Berkeley) 4/19/91
.Nd decode a visual representation of characters
.Fn unvis "u_char *cp" "u_char c" "int *astate" "int flag"
.Fn strunvis "char *dst" "char *src"
are used to decode a visual representation of characters, as produced
the original form. Unvis is called with successive characters in
sequence is recognized, at which time the decoded character is
available at the character pointed to by
into the buffer pointed to by
decoding any escape sequences along the way,
and returns the number of characters placed into
invalid escape sequence was detected. The size of
(that is, no expansion takes place during
implements a state machine that can be used to decode an arbitrary
stream of bytes. All state associated with the bytes being decoded
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
with each successive byte, along with a pointer
to this integer, and a pointer to an destination character.
has several return codes that must be handled properly. They are:
.Bl -tag -width UNVIS_VALIDPUSH
Another character is necessary; nothing has been recognized yet.
A valid character has been recognized and is available at the location
A valid character has been recognized and is available at the location
pointed to by cp; however, the character currently passed in should
A valid sequence was detected, but no character was produced. This
return code is necessary to indicate a logical break between characters.
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
one more time with flag set to
to extract any remaining character (the character passed in is ignored).
The following code fragment illustrates a proper use of
.Bd -literal -offset indent
while ((ch = getchar()) != EOF) {
switch(unvis(&out, ch, &state, 0)) {
(void)fprintf(stderr, "bad sequence!\n");
if (unvis(&out, (char)0, &state, UNVIS_END) == UNVIS_VALID)