trusty (3) fread.3posix.gz

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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 unspecified. 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>


       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- 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 .