The atoi and atol functions convert the initial portion of a
    string to its decimal int or long int value, respectively. The
    atoi and atol functions do not account for overflows resulting
    from the conversion. The string to be converted has the following
    format:

    [white-spaces][+|-]digits

    The function call atol (str) is equivalent to strtol (str,
    (char**)NULL, 10), and the function call atoi (str) is equivalent
    to (int) strtol (str, (char**)NULL, 10), except, in both cases,
    for the behavior on error.