Re: Issue using more than 255 color pairs

[Thomas Dickey]

On Sun, Jul 16, 2023 at 12:06:31AM +0200, David Unterwandling wrote:
> In-Reply-To: <ZLK77gvDufh2Rwhb@prl-debianold-64.jexium-island.net>
> References: <ZLK77xDE6pSvXDCB@scw>
>  <ZLK77gvDufh2Rwhb@prl-debianold-64.jexium-island.net>
> 
> 
> > perhaps if you provided a complete test-program which demonstrates an
> > unwanted change, I could investigate that.
> 
> #define _XOPEN_SOURCE 700

_XOPEN_SOURCE is already defined in the compiler's preamble (outside your
source).  Normally you'd do that on the command-line.

> #include <curses.h>
> #include <string.h>
> 
> void main(void)
  ^ (standard C uses "int")

> {   
>     register int i;
>     char *f, *s;
> 
>     initscr();
>     start_color();
>     use_default_colors();
>     
>     sprintf(f, "%d color pairs allowed", COLOR_PAIRS); /* 65536 */

"f" is an uninitialized buffer (and that sprintf trashes memory)

>     s = strdup(f);
>     addstr(s);
>     
>     for (i = 1; i < 300; i++)
>         init_pair(i, -1, COLOR_RED);
>
>     if (!COLOR_PAIR(256))
>         addstr(", but maximum is 256\n");

When "i" is 256, that equals COLORS, and ncurses does something like

        foo = (bar >= 0) ? (bar % COLORS) : -1;
 
so you get 0 (zero).  That's expected (because I have to allow for -1 as
a special out-of-range value).

I could make init_pair return an error, but since you're not checking
for errors, this case wouldn't make a difference.

> #define A_COLOR NCURSES_BITS(((1U) << 16) - 1U, 0)

I suppose you're wondering why you can't make the program work if you are
redefining constants in curses.h ?

By redefining it, you moved your program's sense of where the attribute
and color bits are -- but ncurses didn't move.
 
>     attron(COLOR_PAIR(260));

this line (as seen in ncurses) is
  
      attron(A_STANDOUT | COLOR_PAIR(4));

>     addstr("now these are immutable and have A_REVERSE");
>     
>     refresh();
>     getch();
>     endwin();
> }
> 

-- 
Thomas E. Dickey <dickey@invisible-island.net>
https://invisible-island.net

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