1UNGETWC(3P) POSIX Programmer's Manual UNGETWC(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 ungetwc — push wide-character code back into the input stream
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15 #include <stdio.h>
16 #include <wchar.h>
17 wint_t ungetwc(wint_t wc, FILE *stream);
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21 The functionality described on this reference page is aligned with the
22 ISO C standard. Any conflict between the requirements described here
23 and the ISO C standard is unintentional. This volume of POSIX.1‐2017
24 defers to the ISO C standard.
25 The ungetwc() function shall push the character corresponding to the
27 wide-character code specified by wc back onto the input stream pointed
28 to by stream. The pushed-back characters shall be returned by subse‐
29 quent reads on that stream in the reverse order of their pushing. A
30 successful intervening call (with the stream pointed to by stream) to a
31 file-positioning function (fseek(), fseeko(), fsetpos(), or rewind())
32 or fflush() shall discard any pushed-back characters for the stream.
33 The external storage corresponding to the stream is unchanged.
34 At least one character of push-back shall be provided. If ungetwc() is
36 called too many times on the same stream without an intervening read or
37 file-positioning operation on that stream, the operation may fail.
38 If the value of wc equals that of the macro WEOF, the operation shall
40 fail and the input stream shall be left unchanged.
41 A successful call to ungetwc() shall clear the end-of-file indicator
43 for the stream. The value of the file-position indicator for the stream
44 after all pushed-back characters have been read, or discarded by call‐
45 ing fseek(), fseeko(), fsetpos(), or rewind() (but not fflush()), shall
46 be the same as it was before the characters were pushed back. The file-
47 position indicator is decremented (by one or more) by each successful
48 call to ungetwc(); if its value was 0 before a call, its value is
49 unspecified after the call.
50
52 Upon successful completion, ungetwc() shall return the wide-character
53 code corresponding to the pushed-back character. Otherwise, it shall
54 return WEOF.
55
57 The ungetwc() function may fail if:
58 EILSEQ An invalid character sequence is detected, or a wide-character
60 code does not correspond to a valid character.
61 The following sections are informative.
63
65 None.
66
68 None.
69
71 None.
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74 None.
75
77 Section 2.5, Standard I/O Streams, fseek(), fsetpos(), read(),
78 rewind(), setbuf()
79 The Base Definitions volume of POSIX.1‐2017, <stdio.h>, <wchar.h>
81
83 Portions of this text are reprinted and reproduced in electronic form
84 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
85 table Operating System Interface (POSIX), The Open Group Base Specifi‐
86 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
87 Electrical and Electronics Engineers, Inc and The Open Group. In the
88 event of any discrepancy between this version and the original IEEE and
89 The Open Group Standard, the original IEEE and The Open Group Standard
90 is the referee document. The original Standard can be obtained online
91 at http://www.opengroup.org/unix/online.html .
92 Any typographical or formatting errors that appear in this page are
94 most likely to have been introduced during the conversion of the source
95 files to man page format. To report such errors, see https://www.ker‐
96 nel.org/doc/man-pages/reporting_bugs.html .
97IEEE/The Open Group 2017 UNGETWC(3P)