System

System is the process-control class. At present it offers a single helper, exit, which terminates the program and returns control to DOS.

#import <System.xt>

Methods

static void exit(i16 value);

Terminates the program by jumping through the Atari DOSVEC at $0A/$0B. The 16-bit exit value is stored at $02FD/$02FE (otherwise-unused OS page-2 bytes) for any caller that cares. DOS itself ignores the exit value — it’s there for cooperating callers, not as a process-status mechanism the OS understands.

void main(void)
{
    if (load("data") == 0) {
        Stdio.print("missing data file\n");
        System.exit(1);
    }
    // …normal path…
    System.exit(0);
}

If you don’t call exit, main returning to its caller has the same effect as exit(0) on default-xtc builds: the runtime emits an RTS back into DOS. The difference is that exit works from anywhere in the program — you don’t have to unwind back to main.

The -Q loop command-line switch changes the post-main behaviour to an infinite loop instead of an RTS; in that mode, System.exit(...) is the only way to actually return to DOS.

Platform notes

System is also implemented for the C64 under support/commodore/lib/System.xt, with the same signature. The C64 version returns through the BASIC warm-start vector instead of Atari’s DOSVEC.