seek(2) [netbsd man page]

LSEEK(2)						      BSD System Calls Manual							  LSEEK(2)

NAME

     lseek, seek -- reposition read/write file offset

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

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

DESCRIPTION

     The lseek() function repositions the offset of the file descriptor fildes to the argument offset according to the directive whence.  The
     argument fildes must be an open file descriptor.  lseek() repositions the file pointer fildes as follows:

	   If whence is SEEK_SET, the offset is set to offset bytes.

	   If whence is SEEK_CUR, the offset is set to its current location plus offset bytes.

	   If whence is 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 existing end-of-file of the file.  If data is later written at
     this point, subsequent reads of the data in the gap return bytes of zeros (until data is actually written into the gap).

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

RETURN VALUES

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

ERRORS

     lseek() will fail and the file pointer will remain unchanged if:

     [EBADF]		fildes is not an open file descriptor.

     [EINVAL]		whence is not a proper value, or the resulting file offset would be invalid.

     [ESPIPE]		fildes is associated with a pipe, socket, or FIFO.

SEE ALSO

     dup(2), open(2)

STANDARDS

     The lseek() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').

HISTORY

     A seek() function appeared in Version 2 AT&T UNIX, later renamed into lseek() for ``long seek'' due to a larger offset argument type.

BUGS

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

BSD
								   April 3, 2010							       BSD

lseek(2)							   System Calls 							  lseek(2)

NAME

       lseek - move read/write file pointer

SYNOPSIS

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

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

DESCRIPTION

       The lseek() function sets the file pointer associated with the open file descriptor specified by fildes as follows:

	 o  If whence is SEEK_SET, the pointer is set to offset bytes.

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

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

       The symbolic constants SEEK_SET, SEEK_CUR, and SEEK_END are defined in the header <unistd.h>.

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

       The  lseek() function allows the file pointer to be set beyond the existing data in the file. If data are later written at this point, sub-
       sequent 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.

       If  fildes  is a remote file descriptor and offset is negative, lseek() returns the file pointer  even if it is negative. The lseek() func-
       tion will not, by itself, extend the size of a file.

       If fildes refers to a shared memory object, lseek() behaves as if fildes referred to a regular file.

RETURN VALUES

       Upon successful completion, the resulting offset, as measured in bytes from the beginning of the file, is returned. Otherwise, (off_t)-1 is
       returned, the file offset remains unchanged, and errno is set to indicate the error.

ERRORS

       The lseek() function will fail if:

       EBADF	       The fildes argument is not an open file descriptor.

       EINVAL	       The  whence argument is not SEEK_SET, SEEK_CUR, or SEEK_END; or the fildes argument is not a remote file descriptor and the
		       resulting file pointer would be negative.

       EOVERFLOW       The resulting file offset would be a value which cannot be represented correctly in an object of  type  off_t  for  regular
		       files.

       ESPIPE	       The fildes argument is associated with a pipe, a FIFO, or a socket.

USAGE

       The lseek() function has a transitional interface for 64-bit file offsets.  See lf64(5).

       In  multithreaded  applications,  using lseek() in conjunction with a read(2) or write(2) call on a file descriptor shared by more than one
       thread is not an atomic operation.  To ensure atomicity, use pread() or pwrite().

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       creat(2), dup(2), fcntl(2), open(2), read(2), write(2), attributes(5), lf64(5), standards(5)

SunOS 5.10							    17 Apr 2002 							  lseek(2)