Show a clock and battery percentage in X root tile (for dwm)

dwmclock.c

#define _GNU_SOURCE

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <X11/Xlib.h>

#define ENERGY_FULL "/sys/class/power_supply/BAT0/energy_full"
#define ENERGY_NOW "/sys/class/power_supply/BAT0/energy_now"
#define BAT_REFRESH_SECONDS 60

int stop = 0;

#ifdef BATTERY
int getnum(char *fn)
{
	char buf[1024];
	FILE *f;
	int len;

	f = fopen(fn, "r");
	len = fread(buf, 1, 1023, f);
	if (ferror(f)) {
		return -1;
	}
	fclose(f);
	if (len > 1022 || len < 1) {
		return -1;
	}
	buf[1023] = '\0';

	return atoi(buf);
}
#endif

void handler(int sig)
{
	stop = sig;
}

int main(void)
{
	struct tm *tm;
	time_t now;
#ifdef BATTERY
	int curr, max, a, b, i;
	char name[8 + 9]; /* (p)pp.pp% hh:mm:ss\0 */
	char *perc = name;
	char *clock = name + 8;
#else
	char name[9]; /* hh:mm:ss\0 */
	char *clock = name;
#endif
	struct sigaction act;
	Display *disp;
	int screen;
	Window root;

	act.sa_handler = handler;
	act.sa_flags = 0;
	sigemptyset(&act.sa_mask);
	sigaction(SIGHUP, &act, NULL);
	sigaction(SIGINT, &act, NULL);
	sigaction(SIGQUIT, &act, NULL);
	sigaction(SIGTERM, &act, NULL);


#ifdef BATTERY
	for (i=0; !stop; ++i) {
#else
	while (!stop) {
#endif
		disp = XOpenDisplay(NULL);
		if (!disp) {
			puts("Cannot open display!");
			return 1;
		}
		screen = DefaultScreen(disp);
		root = RootWindow(disp, screen);
#ifdef BATTERY
		if (i % (BAT_REFRESH_SECONDS) == 0) {
			curr = getnum(ENERGY_NOW) / 1000;
			max = getnum(ENERGY_FULL) / 1000;
			if (curr < 0 || max < 1) {
				a = b = -1;
			} else {
				a = (curr * 10000) / max;
				b = a % 100;
				a /= 100;
			}
		}

		if (a < 0 || b < 0) {
			snprintf(perc, 9, "NO BAT ");
		} else if (a < 0 || a > 999999 || b < 0 || b > 99) {
			snprintf(perc, 8, "INVALID", a, b);
		} else if (a > 999) {
			snprintf(perc, 8, "%6d%%", a);
		} else if (a > 99) {
			snprintf(perc, 8, "%3d.%02d%%", a, b);
		} else {
			snprintf(perc, 8, " %2d.%02d%%", a, b);
		}
		perc[7] = ' ';
#endif

		now = time(NULL);
		tm = localtime(&now);
		strftime(clock, 9, "%H:%M:%S", tm);

		XStoreName(disp, root, name);
		XCloseDisplay(disp);
		sleep(1);
	}


	return 0;
}