fread(3) [opendarwin 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)

FREAD(3P)						     POSIX Programmer's Manual							 FREAD(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       fread - binary input

SYNOPSIS

       #include <stdio.h>

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

DESCRIPTION

       The fread() function shall read into the array pointed to by ptr up to nitems elements whose size is specified by size in bytes,  from  the
       stream  pointed to by stream.  For each object, size calls shall be made to the fgetc() function and the results stored, in the order read,
       in an array of unsigned char exactly overlaying the object. The file position indicator for the stream (if defined) shall  be  advanced	by
       the  number  of	bytes successfully read. If an error occurs, the resulting value of the file position indicator for the stream is unspeci-
       fied. If a partial element is read, its value is unspecified.

       The fread() function may mark the st_atime field of the file associated with stream for update. The st_atime  field  shall  be  marked  for
       update  by the first successful execution of fgetc(), fgets(), fgetwc(), fgetws(), fread(), fscanf(), getc(), getchar(), gets(), or scanf()
       using stream that returns data not supplied by a prior call to ungetc() or ungetwc().

RETURN VALUE

       Upon successful completion, fread() shall return the number of elements successfully read which is less than nitems only if a read error or
       end-of-file is encountered. If size or nitems is 0, fread() shall return 0 and the contents of the array and the state of the stream remain
       unchanged. Otherwise, if a read error occurs, the error indicator for the stream shall be set,  and errno shall	be  set  to  indicate  the
       error.

ERRORS

       Refer to fgetc().

       The following sections are informative.

EXAMPLES

   Reading from a Stream
       The following example reads a single element from the fp stream into the array pointed to by buf.

	      #include <stdio.h>
	      ...
	      size_t bytes_read;
	      char buf[100];
	      FILE *fp;
	      ...
	      bytes_read = fread(buf, sizeof(buf), 1, fp);
	      ...

APPLICATION USAGE

       The ferror() or feof() functions must be used to distinguish between an error condition and an end-of-file condition.

       Because	of  possible differences in element length and byte ordering, files written using fwrite() are application-dependent, and possibly
       cannot be read using fread() by a different application or by the same application on a different processor.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       feof(), ferror(), fgetc(), fopen(), getc(), gets(), scanf(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdio.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. 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 http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								 FREAD(3P)