C++ 時間處理-日期時間類

1. 關鍵詞
2. 問題
3. 設計理念
4. 支持的能力
5. 代碼實現
- 5.1. datetime.h
- 5.2. timecount.cpp
6. 測試代碼
7. 運行結果
8. 源碼地址

1. 關鍵詞

C++ 時間處理日期時間類跨平臺

2. 問題

為什么C++就沒有一個方便好用的表示日期時間的類？

同樣是高級語言，Java中有Date，C#中有DateTime，Python中有datetime，為什么C++就沒有一個方便好用的表示日期時間的類？我覺得這是C++ STL的遺憾，在這個點上做的是挺失敗的。C++11之前，處理日期時間一般都會用C語言函數，如：localtime, gmtime, mktime, gettimeofday, put_time等。C++11之后，引入了chrono庫，做到了時間處理的跨平臺化和標準化，時間精度也支持到了納秒級，但是chrono庫的用法非常累贅，一點也不簡潔，如：要以毫秒為單位獲取當前時間戳，他的實現要寫以下這么一長串的代碼。

auto now = std::chrono::system_clock::now();
auto timestamp_ms = std::chrono::duration_cast<std::chrono::milliseconds>(now.time_since_epoch()).count();
auto ms = static_cast<uint64_t>(timestamp_ms);

那~ 有沒有更簡潔、漂亮的實現方式呢？

答案是：自己寫一個！

3. 設計理念

極簡
易用
跨平臺

4. 支持的能力

獲取當前時間
獲取UTC時間
格式化時間
從字符串解析時間
時間差計算
時間精度：毫秒級

5. 代碼實現

5.1. datetime.h

#pragma once#include <cstdint>
#include <string>
#include <iostream>
#include <regex>
#include <vector>
#include <utility>namespace cutl
{/*** @brief the string datetime format for parsing and formatting**/enum class datetime_format{/** YYYY-MM-DD HH:MM:SS.sss */datetime_format_a,/** YYYY.MM.DD HH:MM:SS */datetime_format_b,/** YYYY/MM/DD HH:MM:SS */datetime_format_c,/** YYYYMMDD HH:MM:SS */datetime_format_d,};/*** @brief A simple, feature-rich modern C++ date-time class**/class datetime{public:/*** @brief Constants value: second, expressed in milliseconds.**/static constexpr int second = 1000;/*** @brief Constants value: min, expressed in milliseconds.**/static constexpr int min = 60 * second;/*** @brief Constants value: hour, expressed in milliseconds.**/static constexpr int hour = 60 * min;/*** @brief Constants value: day, expressed in milliseconds.**/static constexpr int day = 24 * hour;public:/*** @brief Construct a new datetime object** @param ms a timestamp in milliseconds for initialize the datetime object*/datetime(uint64_t ms);/*** @brief Construct a new datetime object** @param other other datetime object to copy*/datetime(const datetime &other);/*** @brief Destroy the datetime object**/~datetime();private:datetime();public:/*** @brief Get a datetime object for the current system time** @return datetime object for the current system time*/static datetime now();/*** @brief Constructs a datetime object from a local time string.** Only the following time formats are supported:* - YYYY-MM-DD HH:MM:SS.sss* - YYYY-MM-DD HH:MM:SS* - YYYY.MM.DD HH:MM:SS.sss* - YYYY.MM.DD HH:MM:SS* - YYYY/MM/DD HH:MM:SS.sss* - YYYY/MM/DD HH:MM:SS* - YYYYMMDD HH:MM:SS.sss* - YYYYMMDD HH:MM:SS* @param time_text local time string, use the below formats to construct a datetime object.* @param isdst the setting of daylight saving time, -1 means system automatically determine, 0 means not in daylight saving time, 1 means in daylight saving time* @return datetime object constructed from the local time string*/static datetime get(const std::string &time_text, int isdst = -1);public:/*** @brief Get the timestamp in milliseconds** @return the timestamp in milliseconds*/uint64_t timestamp() const;/*** @brief format the datetime object to a string** @param dfmt datetime format, a value of datetime_format enum, default is datetime_format_a* @param local whether to use local time, default is true. if true means output in local time, otherwise, output in UTC time.* @param show_milliseconds whether to show milliseconds, default is true. if true means show milliseconds, otherwise, not show milliseconds.* @return formatted datetime string described by std::string*/std::string format(datetime_format dfmt = datetime_format::datetime_format_a, bool local = true, bool show_milliseconds = true) const;// fmt, usages like std::put_time/*** @brief Format the datetime object to a string with a custom format string** @param fmt datetime format string, default is "%Y-%m-%d %H:%M:%S.%f". usages like std::put_time, reference to https://en.cppreference.com/w/cpp/io/manip/put_time* @param local whether to use local time, default is true. if true means output in local time, otherwise, output in UTC time.* @param show_milliseconds whether to show milliseconds, default is true. if true means show milliseconds, otherwise, not show milliseconds.* @return formatted datetime string described by std::string*/std::string format(const std::string &fmt, bool local = true, bool show_milliseconds = true) const;/*** @brief Get the string of UTC time described by datetime object** @return the string of UTC time in format "YYYY-MM-DD HH:MM:SS.sss"*/std::string utctime() const{return format(datetime_format::datetime_format_a, false);}/*** @brief Define the assignment operator** @param other other datetime object to copy* @return datetime& the reference of the current datetime object*/datetime &operator=(const datetime &other);/*** @brief Define the addition operator** @param ms milliseconds to add* @return datetime object after adding milliseconds*/datetime operator+(uint64_t ms);/*** @brief Define the subtraction operator** @param ms milliseconds to subtract* @return datetime object after subtracting milliseconds*/datetime operator-(uint64_t ms);/*** @brief Define the addition and assignment operator** @param ms milliseconds to add* @return datetime& the reference of the current datetime object after adding milliseconds*/datetime &operator+=(uint64_t ms);/*** @brief Define the subtraction and assignment operator** @param ms milliseconds to subtract* @return datetime& the reference of the current datetime object after subtracting milliseconds*/datetime &operator-=(uint64_t ms);/*** @brief Define the subtraction operator between two datetime objects** @param other datetime object to subtract* @return the duration in milliseconds between current and other datetime objects*/int64_t operator-(const datetime &other) const;private:using time_regex_type = std::pair<std::string, std::regex>;using time_regex_vec_type = std::vector<time_regex_type>;static std::string supported_time_formats(const time_regex_vec_type &fmtlist);static bool verify_time(const struct tm &time);private:uint64_t timestamp_ms_;};/*** @brief Define the output stream operator for datetime object** @param os the std::ostream object* @param dt the datetime object to be output* @return std::ostream& the reference of the std::ostream object after outputting the datetime object*/std::ostream &operator<<(std::ostream &os, const datetime &dt);} // namespace

5.2. timecount.cpp

#include "datetime.h"
#include "timeutil.h"
#include "strfmt.h"
#include "inner/logger.h"namespace cutl
{datetime::datetime(const datetime &other){timestamp_ms_ = other.timestamp_ms_;}datetime::datetime(){timestamp_ms_ = 0;}datetime::datetime(uint64_t ms) : timestamp_ms_(ms){}datetime::~datetime(){}datetime datetime::now(){return datetime(cutl::timestamp(timeunit::ms));}datetime datetime::get(const std::string &time_text, int isdst){std::smatch matchRes;bool result = false;static time_regex_vec_type fmt_list = {// 0/1, 2/3, 4/5, 6/7的順序不能反，因為不含毫秒數的時間會被優先匹配到std::make_pair("YYYY-MM-DD HH:MM:SS.sss", std::regex(R"((\d{4})-(\d{2})-(\d{2})[ ](\d{2}):(\d{2}):(\d{2}).(\d{3}))")),std::make_pair("YYYY-MM-DD HH:MM:SS", std::regex(R"((\d{4})-(\d{2})-(\d{2})[ ](\d{2}):(\d{2}):(\d{2}))")),std::make_pair("YYYY.MM.DD HH:MM:SS.sss", std::regex(R"((\d{4}).(\d{2}).(\d{2})[ ](\d{2}):(\d{2}):(\d{2}).(\d{3}))")),std::make_pair("YYYY.MM.DD HH:MM:SS", std::regex(R"((\d{4}).(\d{2}).(\d{2})[ ](\d{2}):(\d{2}):(\d{2}))")),std::make_pair("YYYY/MM/DD HH:MM:SS.sss", std::regex(R"((\d{4})/(\d{2})/(\d{2})[ ](\d{2}):(\d{2}):(\d{2}).(\d{3}))")),std::make_pair("YYYY/MM/DD HH:MM:SS", std::regex(R"((\d{4})/(\d{2})/(\d{2})[ ](\d{2}):(\d{2}):(\d{2}))")),std::make_pair("YYYYMMDD HH:MM:SS.sss", std::regex(R"((\d{4})(\d{2})(\d{2})[ ](\d{2}):(\d{2}):(\d{2}).(\d{3}))")),std::make_pair("YYYYMMDD HH:MM:SS", std::regex(R"((\d{4})(\d{2})(\d{2})[ ](\d{2}):(\d{2}):(\d{2}))")),};for (size_t i = 0; i < fmt_list.size(); i++){auto &fmt_text = fmt_list[i].first;auto &fmt_pattern = fmt_list[i].second;result = std::regex_search(time_text, matchRes, fmt_pattern);if (result){CUTL_DEBUG("matched regex: " + fmt_text);break;}}if (!result || matchRes.size() < 7){auto time_fmts = supported_time_formats(fmt_list);CUTL_ERROR("Only the following time formats are supported:\n" + time_fmts);return datetime();}CUTL_DEBUG("matchRes size:" + std::to_string(matchRes.size()) + ", res:" + matchRes[0].str());// 解析毫秒值int ms = 0;if (matchRes.size() == 8){ms = std::stoi(matchRes[7].str());}// 解析tm結構的時間struct tm time = {};if (matchRes.size() >= 7){for (size_t i = 1; i < 7; i++){time.tm_year = std::stoi(matchRes[1]);time.tm_mon = std::stoi(matchRes[2]);time.tm_mday = std::stoi(matchRes[3]);time.tm_hour = std::stoi(matchRes[4]);time.tm_min = std::stoi(matchRes[5]);time.tm_sec = std::stoi(matchRes[6]);time.tm_isdst = isdst;}}if (!verify_time(time)){return datetime();}// 轉換為時間戳time.tm_year -= 1900;time.tm_mon -= 1;auto ret = mktime(&time);if (ret == -1){CUTL_ERROR("mktime() failed");return datetime();}auto s = static_cast<uint64_t>(ret);return datetime(s2ms(s) + ms);}uint64_t datetime::timestamp() const{return timestamp_ms_;}std::string get_format_str(datetime_format fmt){std::string text;switch (fmt){case datetime_format::datetime_format_a: // YYYY-MM-DD HH:MM:SStext = "%Y-%m-%d %H:%M:%S";break;case datetime_format::datetime_format_b: // YYYY.MM.DD HH:MM:SStext = "%Y.%m.%d %H:%M:%S";break;case datetime_format::datetime_format_c: // YYYY/MM/DD HH:MM:SStext = "%Y/%m/%d %H:%M:%S";break;case datetime_format::datetime_format_d: // YYYYMMDD HH:MM:SStext = "%Y%m%d %H:%M:%S";break;default:break;}return text;}std::string datetime::format(datetime_format fmt, bool local, bool show_milliseconds) const{auto fmtstr = get_format_str(fmt);auto s = timestamp_ms_ / 1000;auto ms = timestamp_ms_ % 1000;auto text = fmt_timestamp(s, local, fmtstr);if (show_milliseconds){text += "." + fmt_uint(ms, 3);}return text;}std::string datetime::format(const std::string &fmt, bool local, bool show_milliseconds) const{auto s = timestamp_ms_ / 1000;auto ms = timestamp_ms_ % 1000;auto text = fmt_timestamp(s, local, fmt);if (show_milliseconds){text += "." + fmt_uint(ms, 3);}return text;}datetime &datetime::operator=(const datetime &other){if (this == &other){return *this;}timestamp_ms_ = other.timestamp_ms_;return *this;}datetime datetime::operator+(uint64_t ms){datetime dt(*this);dt.timestamp_ms_ += ms;return dt;}datetime datetime::operator-(uint64_t ms){datetime dt(*this);dt.timestamp_ms_ -= ms;return dt;}datetime &datetime::operator+=(uint64_t ms){timestamp_ms_ += ms;return *this;}datetime &datetime::operator-=(uint64_t ms){timestamp_ms_ -= ms;return *this;}int64_t datetime::operator-(const datetime &other) const{int64_t diff = timestamp_ms_ - other.timestamp_ms_;return diff;}std::string datetime::supported_time_formats(const time_regex_vec_type &fmtlist){std::string time_fmts;for (size_t i = 0; i < fmtlist.size(); i++){time_fmts += fmtlist[i].first + "\n";}return time_fmts;}bool datetime::verify_time(const struct tm &time){// 校驗年if (time.tm_year < 1900){CUTL_ERROR("the year should be >= 1900");return false;}// 校驗月if (time.tm_mon < 1 || time.tm_mon > 12){CUTL_ERROR("the month should be between 1 and 12");return false;}// 校驗日std::vector<int> large_month = {1, 3, 5, 7, 8, 10, 12};if (std::find(large_month.begin(), large_month.end(), time.tm_mon) != large_month.end() && (time.tm_mday < 1 || time.tm_mday > 31)){CUTL_ERROR("the day should be between 1 and 31 for " + std::to_string(time.tm_mon) + " month");return false;}std::vector<int> small_month = {4, 6, 9, 11};if (std::find(small_month.begin(), small_month.end(), time.tm_mon) != small_month.end() && (time.tm_mday < 1 || time.tm_mday > 30)){CUTL_ERROR("the day should be between 1 and 30 for " + std::to_string(time.tm_mon) + " month");return false;}if (time.tm_mon == 2){auto is_leap_year = [](int year){ return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0); };if (is_leap_year(time.tm_year) && (time.tm_mday < 1 || time.tm_mday > 29)){CUTL_ERROR("the day should be between 1 and 29 for " + std::to_string(time.tm_year) + "-" + fmt_uint(time.tm_mon, 2));return false;}if (!is_leap_year(time.tm_year) && (time.tm_mday < 1 || time.tm_mday > 28)){CUTL_ERROR("the day should be between 1 and 28 for " + std::to_string(time.tm_year) + "-" + fmt_uint(time.tm_mon, 2));return false;}}// 校驗時分秒if (time.tm_hour < 0 || time.tm_hour > 23){CUTL_ERROR("the hour should be between 0 and 23");return false;}if (time.tm_min < 0 || time.tm_min > 59){CUTL_ERROR("the minute should be between 0 and 59");return false;}if (time.tm_sec < 0 || time.tm_sec > 59){CUTL_ERROR("the second should be between 0 and 59");return false;}return true;}std::ostream &operator<<(std::ostream &os, const datetime &dt){os << dt.format();return os;}} // namespace

6. 測試代碼

#pragma once#include <iostream>
#include "datetime.h"
#include "common.hpp"void TestDatetimeBasicUsage()
{PrintSubTitle("TestDatetimeBasicUsage");auto now = cutl::datetime::now();std::cout << "current timestamp(ms): " << now.timestamp() << std::endl;std::cout << "current time(UTC time): " << now.utctime() << std::endl;std::cout << "current time(local time): " << now.format() << std::endl;std::cout << "current time(UTC time) format b: " << now.format(cutl::datetime_format::datetime_format_b, false, true) << std::endl;std::cout << "current time(UTC time) format b, don't show milliseconds: " << now.format(cutl::datetime_format::datetime_format_b, false, false) << std::endl;std::cout << "current time(UTC time) format c: " << now.format(cutl::datetime_format::datetime_format_c, false, true) << std::endl;std::cout << "current time(UTC time) format d: " << now.format(cutl::datetime_format::datetime_format_d, false, true) << std::endl;std::cout << "current time(UTC time) custom format 1: " << now.format("%c %Z", false, true) << std::endl;std::cout << "current time(UTC time) custom format 2: " << now.format("%m/%d/%Y/ %H:%M:%S", false, false) << std::endl;
}void TestDatetimeOperator()
{// 運算符重載PrintSubTitle("TestDatetimeOperator");std::cout << "one day == " << cutl::datetime::day << "ms" << std::endl;std::cout << "one hour == " << cutl::datetime::hour << "ms" << std::endl;std::cout << "one minute == " << cutl::datetime::min << "ms" << std::endl;auto now = cutl::datetime::now();std::cout << "current time: " << now << std::endl;auto dt1 = now - cutl::datetime::min;std::cout << "before one minute: " << dt1 << std::endl;// std::cout << "current time 1: " << now << std::endl;auto dt2 = now + cutl::datetime::min;std::cout << "after one minute: " << dt2 << std::endl;// std::cout << "current time 2: " << now << std::endl;now -= (2 * cutl::datetime::hour);std::cout << "before two hours: " << now << std::endl;now += (4 * cutl::datetime::hour);std::cout << "after two hours: " << now << std::endl;auto dt3 = cutl::datetime::get("2024-03-01 10:00:00");auto dt4 = cutl::datetime::get("2024-03-30 14:18:44");auto duration1 = dt4 - dt3;std::cout << "the difference between " << dt3 << " and " << dt4 << " is: " << duration1 << "ms, formatted: " << cutl::fmt_timeduration_ms(duration1) << std::endl;auto duration2 = dt3 - dt4;std::cout << "the difference between " << dt4 << " and " << dt3 << " is: " << duration2 << "ms" << std::endl;
}void TestDatetimeParseString()
{// 字符串解析成時間PrintSubTitle("TestDatetimeParseString");auto dt0 = cutl::datetime::get(" 2024-03-02 14:18:44 ");std::cout << "dt0: " << dt0 << std::endl;auto dt1 = cutl::datetime::get(" 2024-03-02 14:18:44.023 ");std::cout << "dt1: " << dt1 << std::endl;auto dt2 = cutl::datetime::get(" 2024.03.12 14:18:44");std::cout << "dt2: " << dt2 << std::endl;auto dt3 = cutl::datetime::get(" 2024.03.12 14:18:44.003");std::cout << "dt3: " << dt3 << std::endl;auto dt4 = cutl::datetime::get("2024/03/22 14:18:44 ");std::cout << "dt4: " << dt4 << std::endl;auto dt5 = cutl::datetime::get("2024/03/22 14:18:44.200 ");std::cout << "dt5: " << dt5 << std::endl;auto dt6 = cutl::datetime::get("2024/03/23 09:28:04");std::cout << "dt6: " << dt6 << std::endl;auto dt7 = cutl::datetime::get("2024/03/23 09:28:04.276");std::cout << "dt7: " << dt7 << std::endl;// format errorauto dt8 = cutl::datetime::get(" 2024-0322 14:18:44 ");std::cout << "dt8: " << dt8 << std::endl;// mounth errorauto dt9 = cutl::datetime::get(" 2024-13-02 14:18:44 ");std::cout << "dt9: " << dt9 << std::endl;// leap year errorauto dt10 = cutl::datetime::get(" 2023-02-29 14:18:44 ");std::cout << "dt10: " << dt10 << std::endl;// day errorauto dt11 = cutl::datetime::get(" 2024-03-42 14:18:44 ");std::cout << "dt11: " << dt11 << std::endl;// year > 2038auto dt12 = cutl::datetime::get(" 2044-03-02 14:18:44 ");std::cout << "dt12: " << dt12 << std::endl;std::cout << "dt12 timestamp: " << dt12.timestamp() << std::endl;
}void TestDatetime()
{PrintTitle("datetime");TestDatetimeBasicUsage();TestDatetimeOperator();TestDatetimeParseString();
}

7. 運行結果

==============================================datetime==============================================
---------------------------------------TestDatetimeBasicUsage---------------------------------------
current timestamp(ms): 1716129275853
current time(UTC time): 2024-05-19 14:34:35.853
current time(local time): 2024-05-19 22:34:35.853
current time(UTC time) format b: 2024.05.19 14:34:35.853
current time(UTC time) format b, don't show milliseconds: 2024.05.19 14:34:35
current time(UTC time) format c: 2024/05/19 14:34:35.853
current time(UTC time) format d: 20240519 14:34:35.853
current time(UTC time) custom format 1: Sun May 19 14:34:35 2024 UTC.853
current time(UTC time) custom format 2: 05/19/2024/ 14:34:35
----------------------------------------TestDatetimeOperator----------------------------------------
one day == 86400000ms
one hour == 3600000ms
one minute == 60000ms
current time: 2024-05-19 22:34:35.854
before one minute: 2024-05-19 22:33:35.854
after one minute: 2024-05-19 22:35:35.854
before two hours: 2024-05-19 20:34:35.854
after two hours: 2024-05-20 00:34:35.854
the difference between 2024-03-01 10:00:00.000 and 2024-03-30 14:18:44.000 is: 2521124000ms, formatted: 29d:04h:18m:44s.000ms
the difference between 2024-03-30 14:18:44.000 and 2024-03-01 10:00:00.000 is: -2521124000ms
--------------------------------------TestDatetimeParseString---------------------------------------
dt0: 2024-03-02 14:18:44.000
dt1: 2024-03-02 14:18:44.023
dt2: 2024-03-12 14:18:44.000
dt3: 2024-03-12 14:18:44.003
dt4: 2024-03-22 14:18:44.000
dt5: 2024-03-22 14:18:44.200
dt6: 2024-03-23 09:28:04.000
dt7: 2024-03-23 09:28:04.276
[2024-05-19 22:34:35.857][E]]0x7ff844a9b100](cutl) [datetime.cpp:79:get] Only the following time formats are supported:
YYYY-MM-DD HH:MM:SS.sss
YYYY-MM-DD HH:MM:SS
YYYY.MM.DD HH:MM:SS.sss
YYYY.MM.DD HH:MM:SS
YYYY/MM/DD HH:MM:SS.sss
YYYY/MM/DD HH:MM:SS
YYYYMMDD HH:MM:SS.sss
YYYYMMDD HH:MM:SSdt8: 1970-01-01 08:00:00.000
[2024-05-19 22:34:35.857][E]]0x7ff844a9b100](cutl) [datetime.cpp:241:verify_time] the month should be between 1 and 12
dt9: 1970-01-01 08:00:00.000
[2024-05-19 22:34:35.857][E]]0x7ff844a9b100](cutl) [datetime.cpp:268:verify_time] the day should be between 1 and 28 for 2023-02
dt10: 1970-01-01 08:00:00.000
[2024-05-19 22:34:35.858][E]]0x7ff844a9b100](cutl) [datetime.cpp:248:verify_time] the day should be between 1 and 31 for 3 month
dt11: 1970-01-01 08:00:00.000
dt12: 2044-03-02 14:18:44.000
dt12 timestamp: 2340512324000