fwrite(3) [v7 man page]
FREAD(3) Linux Programmer's Manual FREAD(3) NAME
fread, fwrite - binary stream input/output SYNOPSIS
#include <stdio.h> size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream); size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream); DESCRIPTION
The function fread() reads nmemb items of data, each size bytes long, from the stream pointed to by stream, storing them at the location given by ptr. The function fwrite() writes nmemb items of data, each size bytes long, to the stream pointed to by stream, obtaining them from the loca- tion given by ptr. For nonlocking counterparts, see unlocked_stdio(3). RETURN VALUE
On success, fread() and fwrite() return the number of items read or written. This number equals the number of bytes transferred only when size is 1. If an error occurs, or the end of the file is reached, the return value is a short item count (or zero). fread() does not distinguish between end-of-file and error, and callers must use feof(3) and ferror(3) to determine which occurred. ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). +------------------+---------------+---------+ |Interface | Attribute | Value | +------------------+---------------+---------+ |fread(), fwrite() | Thread safety | MT-Safe | +------------------+---------------+---------+ CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89. SEE ALSO
read(2), write(2), feof(3), ferror(3), unlocked_stdio(3) COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. GNU
2015-07-23 FREAD(3)
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fwrite(3C) Standard C Library Functions fwrite(3C) NAME
fwrite - binary output SYNOPSIS
#include <stdio.h> size_t fwrite(const void *ptr, size_t size, size_t nitems, FILE *stream); DESCRIPTION
The fwrite() function writes, from the array pointed to by ptr, up to nitems elements whose size is specified by size, to the stream pointed to by stream. For each object, size calls are made to the fputc(3C) function, taking the values (in order) from an array of unsigned char exactly overlaying the object. The file-position indicator for the stream (if defined) is 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 st_ctime and st_mtime fields of the file will be marked for update between the successful execution of fwrite() and the next successful completion of a call to fflush(3C) or fclose(3C) on the same stream or a call to exit(2) or abort(3C). RETURN VALUES
The fwrite() function returns the number of elements successfully written, which might be less than nitems if a write error is encountered. If size or nitems is 0, fwrite() returns 0 and the state of the stream remains unchanged. Otherwise, if a write error occurs, the error indicator for the stream is set and errno is set to indicate the error. ERRORS
Refer to fputc(3C). USAGE
Because of possible differences in element length and byte ordering, files written using fwrite() are application-dependent, and possibly cannot be read using fread(3C) by a different application or by the same application on a different processor. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
write(2), fclose(3C), ferror(3C), fopen(3C), fread(3C), getc(3C), gets(3C), printf(3C), putc(3C), puts(3C), attributes(5), standards(5) SunOS 5.11 24 Jul 2002 fwrite(3C)