lseek(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 Manual							  lseek(2)

Name
       lseek, tell - move read or write pointer

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

       pos = lseek(d, offset, whence)
       off_t pos;
       int d, whence;
       off_t offset;

       pos = tell(d)
       off_t pos;
       int d;

Description
       The system call moves the file pointer associated with a file or device open for reading or writing.

       The descriptor d refers to a file or device open for reading or writing.  The system call sets the file pointer of d 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.

       Seeking beyond the end of a file and then writing to the file creates a gap or hole that does not occupy physical space and reads as zeros.

       The system call returns the offset of the current byte relative to the beginning of the file associated with the file descriptor.

Environment
   System Five
       If  you	compile  a  program  in  the System Five environment, an invalid whence argument causes SIGSYS to be sent.  This complies with the
       behavior described in the System V Interface Definition (SVID), Issue 1.

Return Values
       Upon successful completion, a long integer (the current file pointer value) is returned.  This pointer is measured in bytes from the begin-
       ning  of  the file, where the first byte is byte 0.  (Note that some devices are incapable of seeking.  The value of the pointer associated
       with such a device is undefined.)  If a value of -1 is returned, errno is set to indicate the error.

Diagnostics
       The system call fails and the file pointer remains unchanged under the following conditions:

       [EBADF]	      The fildes is not an open file descriptor.

       [EINVAL]       The whence is not a proper value.

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

See Also
       dup(2), open(2)

																	  lseek(2)