illumos: manual page: ungetwc.3c

UNGETWC(3C) Standard C Library Functions UNGETWC(3C)

NAME

ungetwc - push wide-character code back into input stream

SYNOPSIS

#include <stdio.h>
#include <wchar.h>

wint_t ungetwc(wint_t wc, FILE *stream);

DESCRIPTION

The ungetwc() function pushes the character corresponding to the wide
character code specified by wc back onto the input stream pointed to by
stream. The pushed-back characters will be returned by subsequent reads
on that stream in the reverse order of their pushing. A successful
intervening call (with the stream pointed to by stream) to a file-
positioning function ( fseek(3C), fsetpos(3C) or rewind(3C)) discards any
pushed-back characters for the stream. The external storage corresponding
to the stream is unchanged.

One character of push-back is guaranteed. If ungetwc() is called too many
times on the same stream without an intervening read or file-positioning
operation on that stream, the operation may fail.

If the value of wc equals that of the macro WEOF, the operation fails and
the input stream is unchanged.

A successful call to ungetwc() clears the end-of-file indicator for the
stream. The value of the file-position indicator for the stream after
reading or discarding all pushed-back characters will be the same as it
was before the characters were pushed back. The file-position indicator
is decremented (by one or more) by each successful call to ungetwc(); if
its value was 0 before a call, its value is indeterminate after the call.

RETURN VALUES

Upon successful completion, ungetwc() returns the wide-character code
corresponding to the pushed-back character. Otherwise it returns WEOF.

ERRORS

The ungetwc() function may fail if:

EILSEQ
An invalid character sequence is detected, or a wide-character
code does not correspond to a valid character.