Question

I’ve always wondered this, and still haven’t found the answer. Whenever we use “cout” or “printf” how exactly is that printed on the screen?. How does the text come out as it does…(probably quite a vague question here, ill work with whatever you give me.). So basically how are those functions made?..is it assembly?, if so where does that begin?. This brings on more questions like how on earth have they made openGl/directx functions..

break it down people break it down.:)

Answer 1

Here’s one scenario, with abbreviations:

1. printf or cout put characters into a buffer in the user program’s address space.
2. Eventually the buffer fills, or perhaps printf asks for the buffer to be emptied early. Either way, the I/O library calls the operating system, which copies the contents of the buffer to its own space.
3. Supposing that the output file is bound to a terminal, the operating system delivers the characters to the terminal application.
4. The terminal app decides that for each character in the buffer, it needs to paint pixels on the screen.
5. The terminal app sets up pixel-painting instructions, and it asks a window manager to do this on its behalf. (On Unix these days this is usually an X server.)
6. The window manager takes the pixels. If the window is actually visible on the screen, the window manager then updates a buffer (called the frame buffer) which holds the visible pixels. The window manager may then notify the operating system, or more likely, the window manager is in cahoots with the operating system and they are sharing the same memory.
7. The next time the screen is refreshed, the hardware sees the new bits in the frame buffer, and it paints the screen differently.
8. Voilà! You have characters on the screen.

It is amazing that the bear dances at all.