I must say that I love these languages too much, (plus assembly but haven't learned yet) and I'm ready to sacrifice other languages such as Java to learn as far as I can in C/C++.
For now I have good understanding of C/C++ and I can use quite SDL and some other libraries as well. But since each library shows the header as the only readable file I don't know the implementation concerning low-level programming (make sound, card, read modem signal,...) so I feel confused.
Any resource, any advice that can help me to know how to go deep in C/C++ are greatly appreciated. I might not want to know, for example, how SDL library was written but I'm in dire need to know how to write at least a SDL wannabe,e.g write myself. What should I need to achieve this ?
The reason that you don't know how to output to the screen and other hardware is that it is pretty much impossible to do yourself. Your program runs in a protected mode where it only has access to its own limited region of memory and cannot use certain processor instructions. When you need to do any kind of IO, you actually need to ask the operating system to do it for you. Screen output is standardized reasonably well with OpenGL, for example, but even then you need to call OS-specific functions to get the OpenGL functions.