How does vi restore terminal content after quitting it?

Question

How does a program like vi or man or any other program replace the terminal content with the program\'s own contents then after quitting those programs they bring back the o

Answer 1

By sending control sequences to the terminal (xterm, vt-220) or using ncurses (like mc).

A ANSI Escape Sequence starts with ESC (\033 octal) [. ; separates Numbers.

C Example that clears the Screen and moves the cursor to 1,1.

#include 

int main()
{
    // clear the terminal
    printf("\033[2J\033[1;1H");
    printf("hello");

}

Example of switchting to alternate Buffer and back (xterm).

#include 
#include 

int main()
{
    printf("\033[?1049h\033[H");
    printf("hello\n");
    sleep(1);
    printf("bye");
    sleep(1);
    printf("\033[?1049l");
}