C++のmktime関数を使いこなす7つの方法

#include <ctime>

time_t mktime(struct tm *timeptr);

#include <iostream>
#include <ctime>

int main() {
    struct tm t;
    time_t t_of_day;

    t.tm_year = 2023 - 1900;  // 年を設定
    t.tm_mon = 3;             // 月を設定 (4月なので3)
    t.tm_mday = 5;            // 日を設定
    t.tm_hour = 23;
    t.tm_min = 59;
    t.tm_sec = 59;
    t.tm_isdst = -1;          // 夏時間はシステムに依存

    t_of_day = mktime(&t);

    std::cout << "The time is " << ctime(&t_of_day);
    return 0;
}

#include <iostream>
#include <ctime>

int main() {
    struct tm t;
    time_t t_of_day;
    int year, month, day;

    std::cout << "Enter year, month, and day: ";
    std::cin >> year >> month >> day;

    t.tm_year = year - 1900;  // 年を設定
    t.tm_mon = month - 1;     // 月を設定（月は0から始まるため）
    t.tm_mday = day;          // 日を設定
    t.tm_hour = 0;
    t.tm_min = 0;
    t.tm_sec = 0;
    t.tm_isdst = -1;          // 夏時間はシステムに依存

    t_of_day = mktime(&t);

    std::cout << "The specified time is: " << ctime(&t_of_day);
    return 0;
}

#include <iostream>
#include <ctime>

int main() {
    struct tm t;
    time_t t_of_day;

    // 不正な日時を設定
    t.tm_year = 2023 - 1900;
    t.tm_mon = 12;  // 存在しない月（0-11が有効）
    t.tm_mday = 32; // 存在しない日
    t.tm_hour = 25; // 存在しない時間
    t.tm_min = 61;  // 存在しない分
    t.tm_sec = 61;  // 存在しない秒
    t.tm_isdst = -1;

    t_of_day = mktime(&t);

    std::cout << "Normalized time: " << ctime(&t_of_day);
    return 0;
}

#include <iostream>
#include <ctime>

int main() {
    time_t now = time(0);
    struct tm t = *localtime(&now);

    t.tm_mday += 100; // 現在から100日後

    time_t future = mktime(&t);

    std::cout << "100 days from now: " << ctime(&future);
    return 0;
}

#include <iostream>
#include <ctime>
#include <map>
#include <string>

int main() {
    std::map<time_t, std::string> events;
    struct tm t;
    std::string event;
    int year, month, day;

    std::cout << "Enter event date (year month day): ";
    std::cin >> year >> month >> day;
    std::cout << "Enter event description: ";
    std::cin.ignore();
    getline(std::cin, event);

    t.tm_year = year - 1900;
    t.tm_mon = month - 1;
    t.tm_mday = day;
    t.tm_hour = 0;
    t.tm_min = 0;
    t.tm_sec = 0;
    t.tm_isdst = -1;  // 夏時間は考慮しない

    time_t event_time = mktime(&t);
    events[event_time] = event;

    std::cout << "Event set for: " << ctime(&event_time) << "Event: " << events[event_time] << std::endl;
    return 0;
}

#include <iostream>
#include <ctime>

int main() {
    struct tm start, end;
    time_t start_time, end_time, diff;

    std::cout << "Enter start date and time (year month day hour minute): ";
    std::cin >> start.tm_year >> start.tm_mon >> start.tm_mday >> start.tm_hour >> start.tm_min;
    std::cout << "Enter end date and time (year month day hour minute): ";
    std::cin >> end.tm_year >> end.tm_mon >> end.tm_mday >> end.tm_hour >> end.tm_min;

    start.tm_year -= 1900;  // 年の調整
    start.tm_mon -= 1;      // 月の調整
    end.tm_year -= 1900;    // 年の調整
    end.tm_mon -= 1;        // 月の調整
    start.tm_sec = end.tm_sec = 0; // 秒は0に設定
    start.tm_isdst = end.tm_isdst = -1; // 夏時間は非考慮

    start_time = mktime(&start);
    end_time = mktime(&end);
    diff = difftime(end_time, start_time);

    std::cout << "The difference in seconds: " << diff << " seconds" << std::endl;
    return 0;
}

#include <iostream>
#include <ctime>
#include <cstdlib>

int main() {
    setenv("TZ", "PST8PDT", 1);  // タイムゾーンをPST（太平洋標準時）に設定
    tzset();

    struct tm t = {};
    t.tm_year = 2023 - 1900;
    t.tm_mon = 9;   // 10月
    t.tm_mday = 1;
    t.tm_hour = 12;
    t.tm_min = 0;
    t.tm_sec = 0;

    time_t local_time = mktime(&t);
    std::cout << "The local time is: " << ctime(&local_time);

    return 0;
}

#include <iostream>
#include <ctime>
#include <sstream>

int main() {
    std::string iso_date = "2023-10-01T14:00:00";
    struct tm t = {};
    std::istringstream ss(iso_date);
    ss >> std::get_time(&t, "%Y-%m-%dT%H:%M:%S");

    if (!ss.fail()) {
        time_t event_time = mktime(&t);
        std::cout << "Event time is: " << ctime(&event_time);
    } else {
        std::cout << "Failed to parse date." << std::endl;
    }

    return 0;
}