Documentation Archive Developer
ADC Home > Reference Library > Reference > Mac OS X > Mac OS X Man Pages


This document is a Mac OS X manual page. Manual pages are a command-line technology for providing documentation. You can view these manual pages locally using the man(1) command. These manual pages come from many different sources, and thus, have a variety of writing styles.

For more information about the manual page format, see the manual page for manpages(5).

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

     lseek -- reposition read/write file offset

     #include <unistd.h>

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

     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 associ-ated associated
     ated with such a device is undefined.

     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.

     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.

     [EINVAL]           The seek location (calculated from offset and whence)
                        is negative.

     [EOVERFLOW]        The seek location is too large to be stored in an
                        object of type off_t.

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

     dup(2), open(2)

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

     The lseek() function conforms to IEEE Std 1003.1-1988 (``POSIX.1'').

4th Berkeley Distribution       April 19, 1994       4th Berkeley Distribution