#define LOGFILE "/tmp/log.txt"
static void logmsg(const char* fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  FILE *out = fopen(LOGFILE, "a");
  if (out) {
    vfprintf(out, fmt, ap);
    fclose(out);
  }
  va_end(ap);
}