1FGETC(3P) POSIX Programmer's Manual FGETC(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 fgetc — get a byte from a stream
13
15 #include <stdio.h>
16 int fgetc(FILE *stream);
18
20 The functionality described on this reference page is aligned with the
21 ISO C standard. Any conflict between the requirements described here
22 and the ISO C standard is unintentional. This volume of POSIX.1‐2017
23 defers to the ISO C standard.
24 If the end-of-file indicator for the input stream pointed to by stream
26 is not set and a next byte is present, the fgetc() function shall
27 obtain the next byte as an unsigned char converted to an int, from the
28 input stream pointed to by stream, and advance the associated file
29 position indicator for the stream (if defined). Since fgetc() operates
30 on bytes, reading a character consisting of multiple bytes (or ``a
31 multi-byte character'') may require multiple calls to fgetc().
32 The fgetc() function may mark the last data access timestamp of the
34 file associated with stream for update. The last data access timestamp
35 shall be marked for update by the first successful execution of
36 fgetc(), fgets(), fread(), fscanf(), getc(), getchar(), getdelim(),
37 getline(), gets(), or scanf() using stream that returns data not sup‐
38 plied by a prior call to ungetc().
39
41 Upon successful completion, fgetc() shall return the next byte from the
42 input stream pointed to by stream. If the end-of-file indicator for
43 the stream is set, or if the stream is at end-of-file, the end-of-file
44 indicator for the stream shall be set and fgetc() shall return EOF. If
45 a read error occurs, the error indicator for the stream shall be set,
46 fgetc() shall return EOF, and shall set errno to indicate the error.
47
49 The fgetc() function shall fail if data needs to be read and:
50 EAGAIN The O_NONBLOCK flag is set for the file descriptor underlying
52 stream and the thread would be delayed in the fgetc() operation.
53 EBADF The file descriptor underlying stream is not a valid file
55 descriptor open for reading.
56 EINTR The read operation was terminated due to the receipt of a sig‐
58 nal, and no data was transferred.
59 EIO A physical I/O error has occurred, or the process is in a back‐
61 ground process group attempting to read from its controlling
62 terminal, and either the calling thread is blocking SIGTTIN or
63 the process is ignoring SIGTTIN or the process group of the
64 process is orphaned. This error may also be generated for
65 implementation-defined reasons.
66 EOVERFLOW
68 The file is a regular file and an attempt was made to read at or
69 beyond the offset maximum associated with the corresponding
70 stream.
71 The fgetc() function may fail if:
73 ENOMEM Insufficient storage space is available.
75 ENXIO A request was made of a nonexistent device, or the request was
77 outside the capabilities of the device.
78 The following sections are informative.
80
82 None.
83
85 If the integer value returned by fgetc() is stored into a variable of
86 type char and then compared against the integer constant EOF, the com‐
87 parison may never succeed, because sign-extension of a variable of type
88 char on widening to integer is implementation-defined.
89 The ferror() or feof() functions must be used to distinguish between an
91 error condition and an end-of-file condition.
92
94 None.
95
97 None.
98
100 Section 2.5, Standard I/O Streams, feof(), ferror(), fgets(), fread(),
101 fscanf(), getchar(), getc(), gets(), ungetc()
102 The Base Definitions volume of POSIX.1‐2017, <stdio.h>
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106 Portions of this text are reprinted and reproduced in electronic form
107 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
108 table Operating System Interface (POSIX), The Open Group Base Specifi‐
109 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
110 Electrical and Electronics Engineers, Inc and The Open Group. In the
111 event of any discrepancy between this version and the original IEEE and
112 The Open Group Standard, the original IEEE and The Open Group Standard
113 is the referee document. The original Standard can be obtained online
114 at http://www.opengroup.org/unix/online.html .
115 Any typographical or formatting errors that appear in this page are
117 most likely to have been introduced during the conversion of the source
118 files to man page format. To report such errors, see https://www.ker‐
119 nel.org/doc/man-pages/reporting_bugs.html .
120IEEE/The Open Group 2017 FGETC(3P)