After all, since only one file will include the header, that code is unnecessary. Here’s the file: ...

Basically once you've put a using namespace std; in your header, and someone has included your header, there's no way to undo the using. This can reduce your options when a name conflict occurs.

Our example image is 24 pixels wide so we want header data to be 3 bytes wide (24-pixels/8-bits = 3 bytes). You can see from the output that my_header.h was successfully created by the script.