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lseek(2) [sunos man page]

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)

Check Out this Related Man Page

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

NAME
lseek - reposition read/write file offset SYNOPSIS
#include <sys/types.h> #include <unistd.h> 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 ('') until data is actually written into the gap. RETURN VALUE
Upon successful completion, lseek() returns the resulting offset location as measured in bytes from the beginning of the file. On error, the value (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 following macros: old new 0 SEEK_SET 1 SEEK_CUR 2 SEEK_END L_SET SEEK_SET L_INCR SEEK_CUR L_XTND SEEK_END Note that file descriptors created by dup(2) or fork(2) share the current 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 3.27 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 2010-09-11 LSEEK(2)
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