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lseek(2) [v7 man page]

LSEEK(2)							System Calls Manual							  LSEEK(2)

lseek, tell - move read/write pointer SYNOPSIS
long lseek(fildes, offset, whence) long offset; long tell(fildes) DESCRIPTION
The file descriptor refers to a file open for reading or writing. The read (resp. write) pointer for the file is set as follows: If whence is 0, the pointer is set to offset bytes. If whence is 1, the pointer is set to its current location plus offset. If whence is 2, the pointer is set to the size of the file plus offset. The returned value is the resulting pointer location. The obsolete function tell(fildes) is identical to lseek(fildes, 0L, 1). Seeking far beyond the end of a file, then writing, creates a gap or `hole', which occupies no physical space and reads as zeros. SEE ALSO
open(2), creat(2), fseek(3) DIAGNOSTICS
-1 is returned for an undefined file descriptor, seek on a pipe, or seek to a position before the beginning of file. BUGS
Lseek is a no-op on character special files. ASSEMBLER
(lseek = 19.) (file descriptor in r0) sys lseek; offset1; offset2; whence Offset1 and offset2 are the high and low words of offset; r0 and r1 contain the pointer upon return. LSEEK(2)

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

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
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