Man Lseek en anglais
LSEEK(2)                   Linux Programmer's Manual                  LSEEK(2)



 

NAME


       lseek - reposition read/write file offset

 

SYNOPSIS


       #include 
       #include 

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

 

DESCRIPTION






       The lseek() function repositions the offset of the open file associated
       with the file descriptor fd to the argument  offset  according  to  the
       directive whence as follows:

       SEEK_SET
              The offset is set to offset bytes.

       SEEK_CUR
              The offset is set to its current location plus offset bytes.

       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 file (but this does not change the size of the file).  If  data  is
       later written at this point, subsequent reads of the data in the gap (a
       "hole") return null bytes ('\0') until data is  actually  written  into
       the gap.

 

RETURN VALUE


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

 

ERRORS


       EBADF  fd is not an open file descriptor.

       EINVAL whence is not  one  of  SEEK_SET,  SEEK_CUR,  SEEK_END;  or  the
              resulting  file offset would be negative, or beyond the end of a
              seekable device.

 

       EOVERFLOW


              The resulting file offset cannot be represented in an off_t.

       ESPIPE fd is associated with a pipe, socket, or FIFO.

 

CONFORMING TO


       SVr4, 4.3BSD, POSIX.1-2001.

 

NOTES


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

       Some  devices are incapable of seeking and POSIX does not specify which
       devices must support lseek().

       On Linux, using lseek() on a tty device returns ESPIPE.

       When converting old code, substitute values for whence with the follow-
       ing macros:


        old       new
       0        SEEK_SET
       1        SEEK_CUR
       2        SEEK_END
       L_SET    SEEK_SET
       L_INCR   SEEK_CUR
       L_XTND   SEEK_END

       SVr1-3 returns long instead of off_t, BSD returns int.

       Note  that file descriptors created by dup(2) or fork(2) share the cur-
       rent file position pointer, so seeking on such files may be subject  to
       race conditions.

 

SEE ALSO


       dup(2), fork(2), open(2), fseek(3), lseek64(3), posix_fallocate(3)

 

COLOPHON


       This  page  is  part of release 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             2001-09-24                          LSEEK(2)