UNGETWC(P) POSIX Programmer's Manual UNGETWC(P)
ungetwc - push wide-character code back into the input stream
wint_t ungetwc(wint_t wc, FILE *stream);
The ungetwc() function shall push the character corresponding to the wide-character code
specified by wc back onto the input stream pointed to by stream. The pushed-back charac-
ters shall 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(), fsetpos(), or rewind()) discards any pushed-back charac-
ters for the stream. The external storage corresponding to the stream is unchanged.
At least one character of push-back shall be provided. 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 shall fail and the input
stream shall be left unchanged.
A successful call to ungetwc() shall clear 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 shall 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 unspecified after the call.
Upon successful completion, ungetwc() shall return the wide-character code corresponding
to the pushed-back character. Otherwise, it shall return WEOF.
The ungetwc() function may fail if:
EILSEQ An invalid character sequence is detected, or a wide-character code does not corre-
spond to a valid character.
The following sections are informative.
fseek() , fsetpos() , read() , rewind() , setbuf() , the Base Definitions volume of
IEEE Std 1003.1-2001, <stdio.h>, <wchar.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 UNGETWC(P)