Section: POSIX Programmer's Manual (3P)
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
--- binary output
size_t fwrite(const void *restrict ptr, size_t size, size_t nitems,
FILE *restrict stream);
The functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here and the
ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.
function shall write, from the array pointed to by
elements whose size is specified by
to the stream pointed to by
For each object,
calls shall be made to the
function, taking the values (in order) from an array of
exactly overlaying the object. The file-position indicator for the
stream (if defined) shall be advanced by the number of bytes
successfully written. If an error occurs, the resulting value of the
file-position indicator for the stream is unspecified.
The last data modification and last file status change timestamps
of the file shall be marked for update between the successful
and the next successful completion of a call to
on the same stream, or a call to
function shall return the number of elements successfully written,
which may be less than
if a write error is encountered. If
shall return 0 and the state of the stream remains unchanged. Otherwise,
if a write error occurs, the error indicator for the stream shall be set,
shall be set to indicate the error.
The following sections are informative.
Because of possible differences in element length and byte ordering,
files written using
are application-dependent, and possibly cannot be read using
by a different application or by the same application on a different
, Standard I/O Streams,
The Base Definitions volume of POSIX.1-2008,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
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