title: What is the fastest way to read and change the first 8 bytes of a file in C++?
body: <p>What is the fastest way to read and change the first 8 bytes of a file in C++?
  I don't want to store the whole file in memory, because if I want to edit the first 8 bytes of a 10GB file the program would be very slow, and is very memory inefficient. Is there a way to first read and then change the first n bytes of a file, without opening the file in memory?</p>