詳細解析C/C++時間相關(guān)的那些函數(shù)

void func() { // 計時 std::chrono::time_point<std::chrono::high_resolution_clock> begin = high_resolution_clock::now(); std::this_thread::sleep_for(std::chrono::milliseconds(20)); auto end = high_resolution_clock::now(); cout << "time " << duration_cast(end - begin).count() << endl;}

template <class _Rep, class _Period = ratio<1>> class duration;

 template <intmax_t N, intmax_t D = 1> class ratio;

using atto = ratio<1, 1000000000000000000LL>;using femto = ratio<1, 1000000000000000LL>;using pico = ratio<1, 1000000000000LL>;using nano = ratio<1, 1000000000>;using micro = ratio<1, 1000000>;using milli = ratio<1, 1000>;using centi = ratio<1, 100>;using deci = ratio<1, 10>;using deca = ratio<10, 1>;using hecto = ratio<100, 1>;using kilo = ratio<1000, 1>;using mega = ratio<1000000, 1>;using giga = ratio<1000000000, 1>;using tera = ratio<1000000000000LL, 1>;using peta = ratio<1000000000000000LL, 1>;using exa = ratio<1000000000000000000LL, 1>;
using nanoseconds = duration<long long, nano>;using microseconds = duration<long long, micro>;using milliseconds = duration<long long, milli>;using seconds = duration<long long>;using minutes = duration<int, ratio<60>>;using hours = duration<int, ratio<3600>>;
using hours2 = duration<int, ratio<3600, 1>>;using hours2 = duration<int, ratio<7200, 2>>;

template <class _To, class _Rep, class _Period, enable_if_t<_Is_duration_v<_To>, int> = 0> constexpr _To duration_cast(const duration<_Rep, _Period>&) noexcept( is_arithmetic_v<_Rep>&& is_arithmetic_v);
template <class _Ty> _INLINE_VAR constexpr bool _Is_duration_v = _Is_specialization_v<_Ty, duration>;
template <class _Ty>_INLINE_VAR constexpr bool is_arithmetic_v = // determine whether _Ty is an arithmetic type is_integral_v<_Ty> || is_floating_point_v<_Ty>;

void func() { auto sec = std::chrono::seconds(10); auto mill = std::chrono::duration_cast<std::chrono::milliseconds>(sec); cout << sec.count() << endl; // 返回多少s cout << mill.count() << endl; // 返回多少ms}輸出：1010000

template <class _Clock, class _Duration = typename _Clock::duration> class time_point;

void func() { std::chrono::time_point<std::chrono::system_clock, std::chrono::milliseconds> tp(std::chrono::seconds(12)); cout << tp.time_since_epoch().count() << endl; std::time_t t = system_clock::to_time_t(tp); cout << "time " << ctime(&t) << endl;}輸出：12000time Thu Jan 1 08:00:12 1970

void func() { time_point tp(seconds(12)); cout << tp.time_since_epoch().count() << endl; time_point tp2 = time_point_cast(tp); cout << tp2.time_since_epoch().count() << endl;}輸出:1200012

now()：表示當(dāng)前時間的time_pointto_time_t()：將time_point轉(zhuǎn)換成time_t秒from_time_t()：將time_t轉(zhuǎn)換成time_point

struct system_clock { // wraps GetSystemTimePreciseAsFileTime/GetSystemTimeAsFileTime using rep = long long;
 using period = ratio_multiply1>, nano>;
 using duration = chrono::duration; using time_point = chrono::time_point; static constexpr bool is_steady = false;
 _NODISCARD static time_point now() noexcept { // get current time return time_point(duration(_Xtime_get_ticks())); }
 _NODISCARD static __time64_t to_time_t(const time_point& _Time) noexcept { // convert to __time64_t return static_cast<__time64_t>(_Time.time_since_epoch().count() / _XTIME_TICKS_PER_TIME_T); }
 _NODISCARD static time_point from_time_t(__time64_t _Tm) noexcept { // convert from __time64_t return time_point(duration(_Tm * _XTIME_TICKS_PER_TIME_T)); }};

struct steady_clock { // wraps QueryPerformanceCounter using rep = long long; using period = nano; using duration = nanoseconds; using time_point = chrono::time_point; static constexpr bool is_steady = true;
 _NODISCARD static time_point now() noexcept { // get current time const long long _Freq = _Query_perf_frequency(); // doesn't change after system boot const long long _Ctr = _Query_perf_counter(); static_assert(period::num == 1, "This assumes period::num == 1."); const long long _Whole = (_Ctr / _Freq) * period::den; const long long _Part = (_Ctr % _Freq) * period::den / _Freq; return time_point(duration(_Whole + _Part)); }};

void func() { // 計時 std::chrono::time_point<std::chrono::steady_clock> begin = steady_clock::now(); std::this_thread::sleep_for(std::chrono::milliseconds(20)); auto end = steady_clock::now(); cout << "time " << duration_cast(end - begin).count() << endl;}

using high_resolution_clock = steady_clock;

clock_t clock(void);

void func() { clock_t start_t = clock(); cout << start_t << " 個時鐘 \n"; for (int i = 0; i < 100000000; i++) { } clock_t end_t = clock(); cout << end_t << " 個時鐘 \n"; cout << "循環(huán)的秒數(shù)：" << (double)(end_t - start_t) / CLOCKS_PER_SEC << endl;}

void func() { // 獲取當(dāng)前時間戳，單位為秒 struct timeval time; gettimeofday(&time, NULL); cout << time.tv_sec << " s \n";}

time_t time(time_t *time);

void func() { // 獲取當(dāng)前時間戳，單位為秒 time_t now = time(NULL); cout << static_cast<int64_t>(now) << " s \n";}

void func() { // 獲取當(dāng)前時間戳，單位為毫秒 struct timeval time; gettimeofday(&time, NULL); cout << time.tv_sec * 1000 + time.tv_usec / 1000 << " ms \n";}

char* ctime(const time_t* time);

day month year hours:minutes:seconds year\n\0。

void func() { time_t now = time(NULL); char* dt = ctime(&now); cout << "cur time is: " << dt;}輸出：Tue Sep 22 22:01:40 2020

struct tm * localtime(const time_t * timer);

struct tm *gmtime(const time_t *time);

struct tm { int tm_sec; // 秒，正常范圍從 0 到 59，但允許至 61 int tm_min; // 分，范圍從 0 到 59 int tm_hour; // 小時，范圍從 0 到 23 int tm_mday; // 一月中的第幾天，范圍從 1 到 31 int tm_mon; // 月，范圍從 0 到 11 int tm_year; // 自 1900 年起的年數(shù) int tm_wday; // 一周中的第幾天，范圍從 0 到 6，從星期日算起 int tm_yday; // 一年中的第幾天，范圍從 0 到 365，從 1 月 1 日算起 int tm_isdst; // 夏令時};

void func() { time_t rawtime = time(NULL); struct tm* ptminfo = localtime(&rawtime); printf("cur time is: %02d-%02d-%02d %02d:%02d:%02d\n", ptminfo->tm_year + 1900, ptminfo->tm_mon + 1, ptminfo->tm_mday, ptminfo->tm_hour, ptminfo->tm_min, ptminfo->tm_sec); ptminfo = gmtime(&rawtime); printf("cur time is: %02d-%02d-%02d %02d:%02d:%02d\n", ptminfo->tm_year + 1900, ptminfo->tm_mon + 1, ptminfo->tm_mday, ptminfo->tm_hour, ptminfo->tm_min, ptminfo->tm_sec);}輸出：cur time is: 2020-09-23 21:27:37cur time is: 2020-09-23 13:27:37

char * asctime ( const struct tm * time );

void func() { time_t rawtime = time(NULL); struct tm* info1 = localtime(&rawtime); cout << "正常 日期和時間：" << asctime(info1) << endl; info1 = gmtime(&rawtime); cout << "UTC 日期和時間：" << asctime(info1) << endl;}輸出：正常 日期和時間：Wed Sep 23 21:47:44 2020UTC 日期和時間：Wed Sep 23 13:47:44 2020

size_t strftime( char *str, // 指向目標(biāo)數(shù)組的指針，用來復(fù)制產(chǎn)生的C字符串 size_t maxsize, // 最多傳出字符數(shù)量 const char *format, // 格式化方式 const struct tm *timeptr // tm指針);

%a 星期幾的縮寫%A 星期幾的全稱%b 月份的縮寫%B 月份的全稱%c 標(biāo)準(zhǔn)的日期的時間串%C 年份的前兩位數(shù)字%d 十進制表示的每月的第幾天（值從1到31）%D 月/天/年%e 在兩字符域中，十進制表示的每月的第幾天%F 年-月-日%g 年份的后兩位數(shù)字，使用基于周的年%G 年份，使用基于周的年%h 簡寫的月份名%H 24小時制的小時（值從0到23）%I 12小時制的小時（值從1到12）%j 十進制表示的每年的第幾天（值從1到366）%m 十進制表示的月份（值從1到12）%M 十時制表示的分鐘數(shù)（值從0到59）%n 換行符%p 本地的AM或PM的等價顯示%r 12小時的時間%R 顯示小時和分鐘：hh:mm%S 十進制的秒數(shù)（值從0到61）%t 水平制表符%T 顯示時分秒：hh:mm:ss%u 每周的第幾天，星期一為第一天 （值從1到7，星期一為1）%U 第年的第幾周，把星期日作為第一天（值從0到53）%V 每年的第幾周，使用基于周的年%w 十進制表示的星期幾（值從0到6，星期天為0）%W 每年的第幾周，把星期一做為第一天（值從0到53）%x 標(biāo)準(zhǔn)的日期串%X 標(biāo)準(zhǔn)的時間串%y 不帶世紀(jì)的十進制年份（值從0到99）%Y 帶世紀(jì)部分的十制年份%Z 時區(qū)名稱，如果不能得到時區(qū)名稱則返回空字符。%% 一個%符號

void func() { time_t rawtime = time(NULL); char buf[256]; strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", localtime(&rawtime)); cout << buf << endl;}