Dealing with memory-mapped I/O

Sometimes, we need to operate on memory in a way that is not conventional or, so to speak, not common. As we've seen, memory is allocated with new and released with delete (or, even better, with make_unique and make_shared). There might be cases in which we need to skip some layer—that is, using a Linux system call; for the sake of performance; or because of a custom behavior that we cannot map with the C++ standard library. This is the case with the mmap Linux system call (man 2 mmap). mmap is a POSIX-compliant system call that allows the programmer to map a file to a portion of memory. Among other things, mmap also allows memory to be allocated, and this recipe will teach you how to do it.

How to do it.....