I once wrote a tool like that but for gnu+linux. You first have to retrieve the memory mapping of the targeted process by reading /proc/<PID>/maps [1] then use process_vm_read/write[2]

[1] http://man7.org/linux/man-pages/man5/proc.5.html

[2] http://man7.org/linux/man-pages/man2/process_vm_readv.2.html