plucky (3) fread.3posix.gz

Provided by: manpages-posix-dev_2017a-2_all bug

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.1‐2017 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 transfers a single 100-byte fixed length record 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.1‐2017, <stdio.h>


       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 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 .

       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 .