Re: [OT] What happens when you clear the screen?
Alex Caracatsanis wrote:
>
> I was reading an old book on C programming for beginners. The author made
> the point that different compilers implement clearing the screen in
> different ways. In an attempt to demonstrate a sort of "universal"
> implementation of screen-clearing, his code printed 25 new-lines, eg:
> while(i < 25) { printf("\n"); i++; } // "push" things off the screen
>
> I know we've got clear_screen(), so we don't need to do any of this, but it
> prompted me to wonder what happens when you clear the screen. What happens
> to characters that may have been "pushed over the top" of the screen? Are
> they lost? Do they still exist somewhere? Can they be "brought back" into
> the screen?
>
> I remember wondering about this in relation to the "active page" vs the
> "display page" - and I don't know if these are connected with the issue
> above - so I guess it's time for me to ask..
>
> Any pointers in the right direction appreciated.
Generally speaking, the lines "pushed off" are not retrivable unless your
application saves them first. Some terminals (and we are talking character-mode
apps here), hold a virtual screen buffer that you can get to using special
terminal escape codes, but this is rare. In the MS-DOS world, there is a fixed
amount of RAM that repesents the screen and characters moved out if this are
lost.
--
Derek Parnell
Melbourne, Australia
Skype name: derek.j.parnell
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