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LSEEK(2)                   Linux Programmer's Manual                  LSEEK(2)



NAME
       lseek - reposition read/write file offset

SYNOPSIS
       #include <&lt;sys/types.h>&gt;
       #include <&lt;unistd.h>&gt;

       off_t lseek(int fd, off_t offset, int whence);

DESCRIPTION
       The lseek() function repositions the offset of the open file associated
       with the file descriptor fd to the argument  offset  according  to  the
       directive whence as follows:

       SEEK_SET
              The offset is set to offset bytes.

       SEEK_CUR
              The offset is set to its current location plus offset bytes.

       SEEK_END
              The offset is set to the size of the file plus offset bytes.

       The lseek() function allows the file offset to be set beyond the end of
       the file (but this does not change the size of the file).  If  data  is
       later written at this point, subsequent reads of the data in the gap (a
       "hole") return null bytes ('\0') until data is  actually  written  into
       the gap.

RETURN VALUE
       Upon  successful completion, lseek() returns the resulting offset loca-
       tion as measured in bytes from the beginning of the file.  Otherwise, a
       value of (off_t) -1 is returned and errno is set to indicate the error.

ERRORS
       EBADF  fd is not an open file descriptor.

       EINVAL whence  is  not  one  of  SEEK_SET,  SEEK_CUR,  SEEK_END; or the
              resulting file offset would be negative, or beyond the end of  a
              seekable device.

       EOVERFLOW
              The resulting file offset cannot be represented in an off_t.

       ESPIPE fd is associated with a pipe, socket, or FIFO.

CONFORMING TO
       SVr4, 4.3BSD, POSIX.1-2001.

NOTES
       This  document's use of whence is incorrect English, but maintained for
       historical reasons.

       Some devices are incapable of seeking and POSIX does not specify  which
       devices must support lseek().

       On Linux, using lseek() on a tty device returns ESPIPE.

       When converting old code, substitute values for whence with the follow-
       ing macros:

       c  c  l  l.    old  new   0    SEEK_SET   1    SEEK_CUR   2    SEEK_END
       L_SET     SEEK_SET L_INCR    SEEK_CUR L_XTND    SEEK_END

       SVr1-3 returns long instead of off_t, BSD returns int.

       Note  that file descriptors created by dup(2) or fork(2) share the cur-
       rent file position pointer, so seeking on such files may be subject  to
       race conditions.

SEE ALSO
       dup(2), fork(2), open(2), fseek(3), lseek64(3), posix_fallocate(3)

COLOPHON
       This  page  is  part of release 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             2001-09-24                          LSEEK(2)