1FWRITE(3P) POSIX Programmer's Manual FWRITE(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 fwrite — binary output
13
15 #include <stdio.h>
16 size_t fwrite(const void *restrict ptr, size_t size, size_t nitems,
18 FILE *restrict stream);
19
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 fwrite() function shall write, from the array pointed to by ptr, up
27 to nitems elements whose size is specified by size, to the stream
28 pointed to by stream. For each object, size calls shall be made to the
29 fputc() function, taking the values (in order) from an array of
30 unsigned char exactly overlaying the object. The file-position indica‐
31 tor for the stream (if defined) shall be advanced by the number of
32 bytes successfully written. If an error occurs, the resulting value of
33 the file-position indicator for the stream is unspecified.
34 The last data modification and last file status change timestamps of
36 the file shall be marked for update between the successful execution of
37 fwrite() and the next successful completion of a call to fflush() or
38 fclose() on the same stream, or a call to exit() or abort().
39
41 The fwrite() function shall return the number of elements successfully
42 written, which may be less than nitems if a write error is encountered.
43 If size or nitems is 0, fwrite() shall return 0 and the state of the
44 stream remains unchanged. Otherwise, if a write error occurs, the error
45 indicator for the stream shall be set, and errno shall be set to indi‐
46 cate the error.
47
49 Refer to fputc().
50 The following sections are informative.
52
54 None.
55
57 Because of possible differences in element length and byte ordering,
58 files written using fwrite() are application-dependent, and possibly
59 cannot be read using fread() by a different application or by the same
60 application on a different processor.
61
63 None.
64
66 None.
67
69 Section 2.5, Standard I/O Streams, ferror(), fopen(), fprintf(),
70 putc(), puts(), write()
71 The Base Definitions volume of POSIX.1‐2017, <stdio.h>
73
75 Portions of this text are reprinted and reproduced in electronic form
76 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
77 table Operating System Interface (POSIX), The Open Group Base Specifi‐
78 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
79 Electrical and Electronics Engineers, Inc and The Open Group. In the
80 event of any discrepancy between this version and the original IEEE and
81 The Open Group Standard, the original IEEE and The Open Group Standard
82 is the referee document. The original Standard can be obtained online
83 at http://www.opengroup.org/unix/online.html .
84 Any typographical or formatting errors that appear in this page are
86 most likely to have been introduced during the conversion of the source
87 files to man page format. To report such errors, see https://www.ker‐
88 nel.org/doc/man-pages/reporting_bugs.html .
89IEEE/The Open Group 2017 FWRITE(3P)