How to keep STDIN at bottom the terminal in C

Question

I am writing a simple instant messaging client in c. It's currently working well, however if a user is typing and receives a message while typing, the message displays AFTER the text, then the user continues on the line below. It would look like this:

USER: I am trying to ty...FRIEND: Hello

pe a message. <--- (the end of the users message)

My idea is:

Somehow force the current data from stdin and load it into a buffer, then use a \r before printing FRIEND: to erase what is on the line, then print from the buffer. Does anyone have any concrete examples of how to accomplish this task?

The final result should be

FRIEND: Hello

USER: I am trying to type a message

The user started typing the message, received a message, the stdin line was shifted downwards, then the user completed their message.

Note: I am running GNOME Terminal 3.6.2 on the newest version of Linux Mint

Answer 1

The usual way to do this is using ncurses (any flavor of curses would work), accepting the input in one window and writing the result to another. Here is a short example:

#include <curses.h>

int
main(void)
{
    bool done = FALSE;
    WINDOW *input, *output;
    char buffer[1024];

    initscr();
    cbreak();
    echo();
    input = newwin(1, COLS, LINES - 1, 0);
    output = newwin(LINES - 1, COLS, 0, 0);
    wmove(output, LINES - 2, 0);    /* start at the bottom */
    scrollok(output, TRUE);
    while (!done) {
    mvwprintw(input, 0, 0, "> ");
    if (wgetnstr(input, buffer, COLS - 4) != OK) {
        break;
    }
    werase(input);
    waddch(output, '\n');   /* result from wgetnstr has no newline */
    waddstr(output, buffer);
    wrefresh(output);
    done = (*buffer == 4);  /* quit on control-D */
    }
    endwin();
    return 0;
}

If you want to learn about VT100 control codes (as distinct from ECMA-48), vt100.net has manuals for some terminals.

Regarding the link VT100 control codes: that is a source of misinformation, as noted in the ncurses FAQ How do I get color with VT100?