//
// coms -- Find serial (COM) ports and notify when they come and go.
//
// - This tool is especially useful with USB virtual serial ports.
// - Run once and terminate with ctrl^c or let it run indefinitely.
//
// 06-Oct-2010 tvb www.LeapSecond.com/tools
//

#include <memory.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define WIN32_LEAN_AND_MEAN
#include <windows.h>

char buf[32*1024];
#define MAX_COM 256

void main()
{
    int n, size, port;
    char now[MAX_COM], then[MAX_COM], *p;

    memset(then, 0, MAX_COM);
    while (1) {

        // Get list of all device names.

        n = QueryDosDeviceA(NULL, buf, sizeof buf);
        if (n == 0) {
            fprintf(stderr, "QueryDosDevice failed\n");
            exit(1);
        }

        // Find defined COM ports in the list.

        memset(now, 0, MAX_COM);
        for (p = buf; n > 0; p += size, n -= size) {
            if (strncmp(p, "COM", 3) == 0) {
                port = atoi(&p[3]);
                if (port > 0 && port < MAX_COM) {
                    now[port] = 1;
                }
            }
            size = strlen(p) + 1;
        }

        // Look for changes in COM port numbers.

        if (memcmp(then, now, MAX_COM) != 0) {
            for (port = 0; port < MAX_COM; port += 1) {
                if (then[port] - now[port]) {
                    printf("%s", now[port] ? "+" : "-");
                }
                if (then[port] + now[port]) {
                    printf("COM%d ", port);
                }
            }
            printf("\n");
            memcpy(then, now, MAX_COM);     // cp now then
        }

        // Wait a second and check again for changes.

        _sleep(1000);
    }
}