pwrite64() shall write count bytes from buf to the file associated with the open file descriptor fd, at the position specified by offset, without changing the file position.
pwrite64() is a large-file version of the pwrite() function as defined in POSIX 1003.1-2001 (ISO/IEC 9945-2003). It differs from pwrite() in that the offset parameter is an off64_t instead of an off_t
On success, pwrite64() shall return the number
of bytes actually written. Otherwise pwrite()
shall return -1 and
errno to indicate the error.