How do I scroll a message across the terminal?

Question

I'm trying to write a program to that acts as a marquee that uses the curses.h library to create a side-scrolling display.

What should happen is that my message "Hello" should appear to scroll from the right side of the terminal to the left, character by character.

"hello" should appear to scroll across the terminal like so:

|                                              H| // fist frame of animation

|                                             He| //2nd

|                                            Hel| //3rd
                                                  ...
|             Hello                             | // some time in the middle of animation

|Hello                                          | // finished.

Instead of appearing to scroll across the terminal my program simply outputs the "Hello" message on the left side of the terminal as if it is finished.

I thought that printing the appropriate number of spaces then the appropriate number of characters of the string each frame would work.

What am I doing wrong?

Below is my code so far:

#include    <curses.h>
#include    <string.h> 
main()
{
    char    message[] = "Hello";
    int     max_y, max_x; // max dimensions of terminal window
    int     text_length;
    int     i,row=0,col=0,spaces=0;

    // Get text length
    text_length = strlen(message);

    // Get terminal dimensions
    getmaxyx(stdscr, max_y, max_x);

    // num of spaces needed to print
    spaces = max_x -1; 

    initscr(); // initialize curses
    clear(); // clear screen to begin

    while(1)
    {
        clear(); // clear last drawn iteration
        move(5,col);
        // print spaces as necessary
        for(i=0;i<spaces;i++)
        {
            addch(' ');
        }
        refresh();
        // print appropriate number of characters of the message            
        for(i=0;i<text_length || i<max_x; i++)
        {
            addch(message[i]);
        }
        refresh();          
        usleep(50000); // wait some time
        spaces = spaces-1; //adjust spaces need for next iteration
    }
}

Answer 1

The first problem is that you call getmaxyx() before initscr(). In this situation, stdscr has not been initialized, so the values returned by getmaxyx() are meaningless. (I get -1 for each value, aka ERR.)

That fixed, the program basically works, but prints junk after the "Hello" string. You can solve that by changing the for loop test, text_length || i<max_x, to text_length && i<max_x, although the result is still probably not quite what you want. But I'll leave it to you to figure that one out.

Finally, as a stylistic matter, I'd suggest using curses' own napms() function instead of usleep() (i.e., napms(50) instead of usleep(50000)). But if you do stick with usleep(), you should add #include <unistd.h> at the top.