lseek(2)                                                              lseek(2)



NAME
     lseek, lseek64 - move read/write file pointer

C SYNOPSIS
     #include <sys/types.h>
     #include <unistd.h>

     offt lseek (int fildes, offt offset, int whence);

     off64t lseek64 (int fildes, off64t offset, int whence);

DESCRIPTION
     fildes is a file descriptor returned from a creat, open, dup, fcntl,
     pipe, or ioctl system call.  lseek and lseek64 set the file pointer
     associated with fildes as follows:

          If whence is SEEKSET, the pointer is set to offset bytes.

          If whence is SEEKCUR, the pointer is set to its current location
                plus offset.

          If whence is SEEKEND, the pointer is set to the size of the file
                plus offset.

     On success, lseek returns the resulting pointer location, as measured in
     bytes from the beginning of the file.  Note that for file descriptors
     that correspond to regular files or directories, lseek does not allow
     negative file offsets.  For device special files, the allowable offset
     values are determined by the individual device drivers.

     lseek allows the file pointer to be set beyond the existing data in the
     file. If data are later written at this point, subsequent reads in the
     gap between the previous end of data and the newly written data will
     return bytes of value 0 until data are written into the gap.

     lseek64 is identical in behavior to lseek except that the type of offset
     is off64t instead of offt . The 64-bit offset value is useful for files
     in XFS filesystems as well as in devices larger than 2 gigabytes in size,
     such as large disks or volumes.

     lseek fails and the file pointer remains unchanged if one or more of the
     following are true:

     EBADF          fildes is not an open file descriptor.

     ESPIPE         fildes is associated with a pipe, fifo, or socket.

     EINVAL         whence is not SEEKSET, SEEKCUR, or SEEKEND.  The
                    process also gets a SIGSYS signal.






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lseek(2)                                                              lseek(2)



     EINVAL         fildes corresponds to a regular file or directory and the
                    resulting file pointer would be negative.

     Some devices are incapable of seeking.  The value of the file pointer
     associated with such a device is undefined.

SEE ALSO
     creat(2), dup(2), fcntl(2), open(2).

DIAGNOSTICS
     Upon successful completion, a non-negative integer indicating the file
     pointer value is returned.  Otherwise, a value of -1 is returned and
     errno is set to indicate the error.  For lseek, the return value type is
     offt; for lseek64, the return value type is off64t.









































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