lseek.2

操作系统设计与实现源码

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


NAME
     lseek - move read/write pointer

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

     #define SEEK_SET     0      /* offset is absolute */
     #define SEEK_CUR     1      /* relative to current position */
     #define SEEK_END     2      /* relative to end of file */

     off_t lseek(int d, off_t offset, int whence)

DESCRIPTION
     The descriptor d refers to a file  or  device  open  for  reading  and/or
     writing.  Lseek sets the file pointer of d as follows:

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

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

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

     Upon successful completion, the resulting pointer location as measured in
     bytes from beginning of the file is returned.  Some devices are incapable
     of seeking.  The value of the pointer associated with such  a  device  is
     undefined.

NOTES
     Seeking far beyond the end of a file, then  writing,  creates  a  gap  or
     "hole", which occupies no physical space and reads as zeros.

RETURN VALUE
     Upon successful completion, the current file pointer value  is  returned.
     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.

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

     [EINVAL]       Whence is not a proper value.





4BSD                            February 24, 1986                            1



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


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

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














































4BSD                            February 24, 1986                            2