LSEEK(2) System Calls Manual LSEEK(2)NAME
lseek, tell - move read/write pointer
long lseek(fildes, offset, whence)
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.
Lseek is a no-op on character special files.
(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.
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LSEEK(2) BSD System Calls Manual LSEEK(2)NAME
lseek -- reposition read/write file offset
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 argu-
ment 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.
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.
[ESPIPE] Fildes is associated with a pipe, socket, or FIFO.
[EINVAL] Whence is not a proper value.
SEE ALSO dup(2), open(2)BUGS
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
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