huschi.net

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  corresponding
       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 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.
       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 posi-
       tion 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 unspecified.  If
       a partial element is read, its value is unspecified.
       The  fread()  function  may  mark the last data access timestamp of the
       file associated with stream for update. The last data access  timestamp
       shall  be  marked  for  update  by  the  first  successful execution of
       fgetc(), fgets(), fread(),  fscanf(),  getc(),  getchar(),  getdelim(),
       getline(),  gets(),  or scanf() using stream that returns data not sup-
       plied by a prior call to ungetc().
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  indica-
       tor 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 elements_read;
           char buf[100];
           FILE *fp;
           ...
           elements_read = fread(buf, sizeof(buf), 1, fp);
           ...
       If  a  read  error occurs, elements_read will be zero but the number of
       bytes  read  from  the  stream  could  be   anything   from   zero   to
       sizeof(buf)-1.
       The  following  example reads multiple single-byte elements 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, 1, sizeof(buf), fp);
           ...
       If a read error occurs, bytes_read will contain  the  number  of  bytes
       read from the stream.
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
       Section  2.5, Standard I/O Streams, feof(), ferror(), fgetc(), fopen(),
       fscanf(), getc(), gets()
       The Base Definitions volume of POSIX.1-2008, <stdio.h>
COPYRIGHT
       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 Electri-
       cal 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 http://www.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                            FREAD(3P)