Section: POSIX Programmer's Manual (3P)
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
--- push wide-character code back into the input stream
wint_t ungetwc(wint_t wc, FILE *stream);
The functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here and the
ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.
function shall push the character corresponding to the wide-character
code specified by
back onto the input stream pointed to by
The pushed-back characters 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
to a file-positioning function (fseek(),
shall discard any pushed-back characters for the stream. The external
storage corresponding to the stream is unchanged.
At least one character of push-back shall be provided. If
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
equals that of the macro WEOF, the operation shall fail and the input
stream shall be left unchanged.
A successful call to
shall clear the end-of-file indicator for the stream. The value of the
file-position indicator for the stream after all pushed-back characters
have been read, or discarded by calling
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
if its value was 0 before a call, its value is unspecified after the call.
Upon successful completion,
shall return the wide-character code corresponding to the pushed-back
character. Otherwise, it shall return WEOF.
function may fail if:
An invalid character sequence is detected, or a wide-character code
does not correspond to a valid character.
The following sections are informative.
, Standard I/O Streams,
The Base Definitions volume of POSIX.1-2017,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 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 original Standard can be obtained online at
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