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FSEEK(3P)                  POSIX Programmer's Manual                 FSEEK(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
       fseek, fseeko -- reposition a file-position indicator in a stream
SYNOPSIS
       #include <stdio.h>
       int fseek(FILE *stream, long offset, int whence);
       int fseeko(FILE *stream, off_t offset, int whence);
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  fseek()  function  shall  set  the file-position indicator for the
       stream pointed to by stream.  If a read  or  write  error  occurs,  the
       error indicator for the stream shall be set and fseek() fails.
       The  new  position,  measured  in bytes from the beginning of the file,
       shall be obtained by adding offset to the position specified by whence.
       The specified point is the beginning of the file for SEEK_SET, the cur-
       rent value of the file-position indicator for SEEK_CUR, or  end-of-file
       for SEEK_END.
       If the stream is to be used with wide-character input/output functions,
       the application shall ensure  that  offset  is  either  0  or  a  value
       returned by an earlier call to ftell() on the same stream and whence is
       SEEK_SET.
       A successful call to fseek() shall clear the end-of-file indicator  for
       the  stream  and undo any effects of ungetc() and ungetwc() on the same
       stream. After an fseek() call, the next operation on an  update  stream
       may be either input or output.
       If  the most recent operation, other than ftell(), on a given stream is
       fflush(), the file offset in the underlying open file description shall
       be adjusted to reflect the location specified by fseek().
       The  fseek() function shall allow the file-position indicator to be set
       beyond the end of existing data in the file. If data is  later  written
       at  this  point, subsequent reads of data in the gap shall return bytes
       with the value 0 until data is actually written into the gap.
       The behavior of fseek() on devices which are incapable  of  seeking  is
       implementation-defined.   The  value of the file offset associated with
       such a device is undefined.
       If the stream is writable and buffered data had not been written to the
       underlying  file,  fseek() shall cause the unwritten data to be written
       to the file and shall mark the last data  modification  and  last  file
       status change timestamps of the file for update.
       In a locale with state-dependent encoding, whether fseek() restores the
       stream's shift state is implementation-defined.
       The fseeko() function shall  be  equivalent  to  the  fseek()  function
       except that the offset argument is of type off_t.
RETURN VALUE
       The fseek() and fseeko() functions shall return 0 if they succeed.
       Otherwise, they shall return -1 and set errno to indicate the error.
ERRORS
       The  fseek() and fseeko() functions shall fail if, either the stream is
       unbuffered or the stream's buffer needed to be flushed, and the call to
       fseek()  or  fseeko()  causes  an  underlying  lseek() or write() to be
       invoked, and:
       EAGAIN The O_NONBLOCK flag is set  for  the  file  descriptor  and  the
              thread would be delayed in the write operation.
       EBADF  The  file  descriptor underlying the stream file is not open for
              writing or the stream's buffer needed to be flushed and the file
              is not open.
       EFBIG  An  attempt  was  made  to write a file that exceeds the maximum
              file size.
       EFBIG  An attempt was made to write a file that exceeds the  file  size
              limit of the process.
       EFBIG  The  file  is a regular file and an attempt was made to write at
              or beyond the offset maximum associated with  the  corresponding
              stream.
       EINTR  The  write operation was terminated due to the receipt of a sig-
              nal, and no data was transferred.
       EINVAL The whence argument  is  invalid.  The  resulting  file-position
              indicator would be set to a negative value.
       EIO    A physical I/O error has occurred, or the process is a member of
              a background process group attempting to perform  a  write()  to
              its  controlling  terminal, TOSTOP is set, the calling thread is
              not blocking SIGTTOU, the process is not ignoring  SIGTTOU,  and
              the  process  group  of the process is orphaned.  This error may
              also be returned under implementation-defined conditions.
       ENOSPC There was no free space remaining on the device  containing  the
              file.
       EOVERFLOW
              For  fseek(),  the  resulting file offset would be a value which
              cannot be represented correctly in an object of type long.
       EOVERFLOW
              For fseeko(), the resulting file offset would be a  value  which
              cannot be represented correctly in an object of type off_t.
       EPIPE  An  attempt was made to write to a pipe or FIFO that is not open
              for reading by any process; a SIGPIPE signal shall also be  sent
              to the thread.
       ESPIPE The file descriptor underlying stream is associated with a pipe,
              FIFO, or socket.
       The fseek() and fseeko() functions may fail if:
       ENXIO  A request was made of a nonexistent device, or the  request  was
              outside the capabilities of the device.
       The following sections are informative.
EXAMPLES
       None.
APPLICATION USAGE
       None.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       Section  2.5,  Standard I/O Streams, fopen(), fsetpos(), ftell(), getr-
       limit(), lseek(), rewind(), ulimit(), ungetc(), write()
       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                            FSEEK(3P)