Compiling and linking C
So, if you are new to programming Compiling and linking can seem like magic. The compiler transforms C source code files into obj files. The actual format is different depending on the CPU and Operating system. Linking is even more magic because it takes a bunch of obj files and produces a single executable.
There’s actual more magic going on than my simplistic explanation. The compiler might be doing optimisation (generally in release mode but not debug). That makes debug compiles faster which is more desirable.
Another blog called Hack the developer has published an article with a lot more detail about compiling and linking. If you want to get a better understanding then this is a petty good piece. It uses Linux, GCC and Clang as examples. It also goes into more depth on the layout of obj files.