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  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 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 supplied 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  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 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  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 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.kernel.org/doc/man-pages/reporting_bugs.html .