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C standard library - < time h＞

2022-04-23 02:04:00 【Huang Jiajun】

brief introduction

time.h The header file defines four variable types 、 Two macros and various functions of operation date and time .

Library variables

Here's the header file time.h Variable types defined in ：

Serial number	Variable & describe
1	size_t Is an unsigned integer type , It is sizeof Keyword results .
2	clock_t This is a type suitable for storage processor time .
3	time_t is This is a type suitable for storing calendar time .
4	struct tm This is a structure for saving time and date .

tm The definition of structure is as follows ：

struct tm {
   int tm_sec;         /*  second , Range from  0  To  59        */
   int tm_min;         /*  branch , Range from  0  To  59        */
   int tm_hour;        /*  Hours , Range from  0  To  23        */
   int tm_mday;        /*  The day of the month , Range from  1  To  31    */
   int tm_mon;         /*  month , Range from  0  To  11        */
   int tm_year;        /*  since  1900  The number of years since         */
   int tm_wday;        /*  The day of the week , Range from  0  To  6    */
   int tm_yday;        /*  The day of the year , Range from  0  To  365    */
   int tm_isdst;       /*  Daylight saving time                 */
};

Library macro

Here's the header file time.h Macro defined in ：

Serial number	macro & describe
1	NULL This macro is the value of a null pointer constant .
2	CLOCKS_PER_SEC This macro represents the number of processor clocks per second .

Library function

Here's the header file time.h The function defined in ：

Serial number	function & describe
1	char asctime(const struct tm timeptr) Returns a pointer to a string , It represents the structure timeptr The date and time of .
2	clock_t clock(void) Return to the beginning of program execution （ It's usually the beginning of a program ）, The time used by the processor clock .
3	char ctime(const time_t timer) Returns a string representing the local time , Local time is based on parameters timer.
4	double difftime(time_t time1, time_t time2) return time1 and time2 The number of seconds between (time1-time2).
5	struct tm gmtime(const time_t timer) timer The value of is decomposed into tm structure , And use coordinated universal time （UTC） Also known as Greenwich mean time （GMT） Express .
6	struct tm localtime(const time_t timer) timer The value of is decomposed into tm structure , And expressed in local time zone .
7	time_t mktime(struct tm *timeptr) hold timeptr The structure pointed to is converted to a structure based on the local time zone time_t value .
8	size_t strftime(char str, size_t maxsize, const char format, const struct tm *timeptr) according to format Formatting rules defined in , Format structure timeptr Time represented , And store it in str in .
9	time_t time(time_t *timer) Calculate the current calendar time , And code it into time_t Format .