fwrite in Linux and UNIX

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LEARN ABOUT NETBSD

fread

FREAD(3)						   BSD Library Functions Manual 						  FREAD(3)

NAME

     fread, fwrite -- binary stream input/output

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <stdio.h>

     size_t
     fread(void * restrict ptr, size_t size, size_t nmemb, FILE * restrict stream);

     size_t
     fwrite(const void * restrict ptr, size_t size, size_t nmemb, FILE * restrict stream);

DESCRIPTION

     The function fread() reads nmemb objects, each size bytes long, from the stream pointed to by stream, storing them at the location given by
     ptr.

     The function fwrite() writes nmemb objects, each size bytes long, to the stream pointed to by stream, obtaining them from the location given
     by ptr.

     Mixing fread() and fwrite() calls without setting the file position explicitly using fsetpos(3) between read and write or write and read
     operations will lead to unexpected results because of buffering the file pointer not being set to the expected position after each operation
     completes.  This behavior is allowed by ANSI C for efficiency and it will not be changed.

RETURN VALUES

     The functions fread() and fwrite() advance the file position indicator for the stream by the number of bytes read or written.  They return
     the number of objects read or written.  If size or nmemb is 0, the functions return 0 and the state of stream remains unchanged.  If an error
     occurs, or the end-of-file is reached, the return value is a short object count (or zero).

     The function fread() does not distinguish between end-of-file and error, and callers must use feof(3) and ferror(3) to determine which
     occurred.	The function fwrite() returns a value less than nmemb only if a write error has occurred.

SEE ALSO

     read(2), write(2)

STANDARDS

     The functions fread() and fwrite() conform to ANSI X3.159-1989 (``ANSI C89'').

BSD
								September 11, 2011							       BSD

Programming