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
13 fwrite — binary output
14
16 #include <stdio.h>
17 size_t fwrite(const void *restrict ptr, size_t size, size_t nitems,
19 FILE *restrict stream);
20
22 The functionality described on this reference page is aligned with the
23 ISO C standard. Any conflict between the requirements described here
24 and the ISO C standard is unintentional. This volume of POSIX.1‐2008
25 defers to the ISO C standard.
26 The fwrite() function shall write, from the array pointed to by ptr, up
28 to nitems elements whose size is specified by size, to the stream
29 pointed to by stream. For each object, size calls shall be made to the
30 fputc() function, taking the values (in order) from an array of
31 unsigned char exactly overlaying the object. The file-position indica‐
32 tor for the stream (if defined) shall be advanced by the number of
33 bytes successfully written. If an error occurs, the resulting value of
34 the file-position indicator for the stream is unspecified.
35 The last data modification and last file status change timestamps of
37 the file shall be marked for update between the successful execution of
38 fwrite() and the next successful completion of a call to fflush() or
39 fclose() on the same stream, or a call to exit() or abort().
40
42 The fwrite() function shall return the number of elements successfully
43 written, which may be less than nitems if a write error is encountered.
44 If size or nitems is 0, fwrite() shall return 0 and the state of the
45 stream remains unchanged. Otherwise, if a write error occurs, the error
46 indicator for the stream shall be set, and errno shall be set to indi‐
47 cate the error.
48
50 Refer to fputc().
51 The following sections are informative.
53
55 None.
56
58 Because of possible differences in element length and byte ordering,
59 files written using fwrite() are application-dependent, and possibly
60 cannot be read using fread() by a different application or by the same
61 application on a different processor.
62
64 None.
65
67 None.
68
70 Section 2.5, Standard I/O Streams, ferror(), fopen(), fprintf(),
71 putc(), puts(), write()
72 The Base Definitions volume of POSIX.1‐2008, <stdio.h>
74
76 Portions of this text are reprinted and reproduced in electronic form
77 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
78 -- Portable Operating System Interface (POSIX), The Open Group Base
79 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
80 cal and Electronics Engineers, Inc and The Open Group. (This is
81 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
82 event of any discrepancy between this version and the original IEEE and
83 The Open Group Standard, the original IEEE and The Open Group Standard
84 is the referee document. The original Standard can be obtained online
85 at http://www.unix.org/online.html .
86 Any typographical or formatting errors that appear in this page are
88 most likely to have been introduced during the conversion of the source
89 files to man page format. To report such errors, see https://www.ker‐
90 nel.org/doc/man-pages/reporting_bugs.html .
91IEEE/The Open Group 2013 FWRITE(3P)