PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       fread — binary input

SYNOPSIS         top

       #include <stdio.h>

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

DESCRIPTION         top

       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         top

       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         top

       Refer to fgetc(3p).

       The following sections are informative.

EXAMPLES         top

   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         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Section 2.5, Standard I/O Streams, feof(3p), ferror(3p), fgetc(3p),
       fopen(3p), fscanf(3p), getc(3p), gets(3p)

       The Base Definitions volume of POSIX.1‐2008, stdio.h(0p)

COPYRIGHT         top

       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 .

IEEE/The Open Group                 2013                           FREAD(3P)