ex9_51.cpp

// Exercise 9.51:
// Write a class that has three unsigned members representing year, month, and day.
// Write a constructor that takes a string representing a date. Your constructor should handle a
// variety of date formats, such as January 1, 1900, 1/1/1900, Jan 1, 1900, and so on.

#include <array>
#include <iostream>
#include <string>

class Date {
public:
    explicit Date(const std::string& str = "");
    void Print();
    unsigned year = 1970;
    unsigned month = 1;
    unsigned day = 1;

private:
    std::array<std::string, 12> month_names{"Jan", "Feb", "Mar", "Apr", "May", "Jun",
                                            "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
    unsigned MonthFromName(const std::string& str);
};

Date::Date(const std::string& str)
{
    if (str.empty()) return;
    std::string delimiters{" ,/"};
    auto month_day_delim_pos = str.find_first_of(delimiters);
    if (month_day_delim_pos == std::string::npos)
        throw std::invalid_argument("This format is not supported now.");
    month = MonthFromName(str.substr(0, month_day_delim_pos));
    auto day_year_delim_pos = str.find_first_of(delimiters, month_day_delim_pos + 1);
    auto day_len = day_year_delim_pos - month_day_delim_pos - 1;
    day = std::stoi(str.substr(month_day_delim_pos + 1, day_len));
    year = std::stoi(str.substr(day_year_delim_pos + 1));
}

void Date::Print()
{
    std::cout << year << "-" << month << "-" << day << "\n";
}

unsigned Date::MonthFromName(const std::string& str)
{
    if (str.empty()) return 0;
    if (std::isdigit(str[0])) return std::stoi(str);
    for (size_t i = 0; i != 12; ++i) {
        if (str.find(month_names[i]) != std::string::npos) return i + 1;
    }
    return 0; //  not found
}

int main()
{
    { //  default case
        auto date = Date();
        date.Print();
    }
    { //  case 0: January 1, 1900
        auto date = Date("January 1, 1900");
        date.Print();
    }
    { //  case 1: 1/1/1900
        auto date = Date("1/1/1900");
        date.Print();
    }
    { //  case 2: Jan 1, 1900
        auto date = Date("Jan 1, 1900");
        date.Print();
    }
}