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.