1UNGETC(3P) POSIX Programmer's Manual UNGETC(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
13 ungetc — push byte back into input stream
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16 #include <stdio.h>
17 int ungetc(int c, 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.1‐2008
24 defers to the ISO C standard.
25 The ungetc() function shall push the byte specified by c (converted to
27 an unsigned char) back onto the input stream pointed to by stream. The
28 pushed-back bytes shall be returned by subsequent reads on that stream
29 in the reverse order of their pushing. A successful intervening call
30 (with the stream pointed to by stream) to a file-positioning function
31 (fseek(), fseeko(), fsetpos(), or rewind()) or fflush() shall discard
32 any pushed-back bytes for the stream. The external storage correspond‐
33 ing to the stream shall be unchanged.
34 One byte of push-back shall be provided. If ungetc() is called too many
36 times on the same stream without an intervening read or file-position‐
37 ing operation on that stream, the operation may fail.
38 If the value of c equals that of the macro EOF, the operation shall
40 fail and the input stream shall be left unchanged.
41 A successful call to ungetc() shall clear the end-of-file indicator for
43 the stream. The value of the file-position indicator for the stream
44 after all pushed-back bytes have been read, or discarded by calling
45 fseek(), fseeko(), fsetpos(), or rewind() (but not fflush()), shall be
46 the same as it was before the bytes were pushed back. The file-position
47 indicator is decremented by each successful call to ungetc(); if its
48 value was 0 before a call, its value is unspecified after the call.
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51 Upon successful completion, ungetc() shall return the byte pushed back
52 after conversion. Otherwise, it shall return EOF.
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55 No errors are defined.
56 The following sections are informative.
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60 None.
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63 None.
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66 None.
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69 None.
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72 Section 2.5, Standard I/O Streams, fseek(), getc(), fsetpos(), read(),
73 rewind(), setbuf()
74 The Base Definitions volume of POSIX.1‐2008, <stdio.h>
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78 Portions of this text are reprinted and reproduced in electronic form
79 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
80 -- Portable Operating System Interface (POSIX), The Open Group Base
81 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
82 cal and Electronics Engineers, Inc and The Open Group. (This is
83 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
84 event of any discrepancy between this version and the original IEEE and
85 The Open Group Standard, the original IEEE and The Open Group Standard
86 is the referee document. The original Standard can be obtained online
87 at http://www.unix.org/online.html .
88 Any typographical or formatting errors that appear in this page are
90 most likely to have been introduced during the conversion of the source
91 files to man page format. To report such errors, see https://www.ker‐
92 nel.org/doc/man-pages/reporting_bugs.html .
93IEEE/The Open Group 2013 UNGETC(3P)