c
char *endptr;
long int value = strtol(optarg, &endptr, 10);
if (endptr == optarg || *endptr != '\0') {
    fprintf(stderr, "Error: invalid input string\n");
    exit(1);
}
if (value < INT_MIN || value > INT_MAX) {
    fprintf(stderr, "Error: input value is outside the range of int\n");
    exit(1);
}
horizSubSampling = (int)value;
