typedef int time_t;
time_t clock();
Returns the time used by the processor clock, divided by CLOCKS_PER_SEC
char* ctime(time_t *timer);
Returns a string representing the local time based on the parameter timer
double difftime(time_t endTime, time_t fromTime);
return the endTime - fromTime in seconds
struct tm* gmtime(time_t *timer);
Populate the tm structure with the value of timer , expressed in Coordinated Universal Time (UTC) also known as Greenwich Mean Time (GMT)
struct tm* localtime(time_t *timer);
Fill the tm structure with the value of timer. The value of timer is decomposed into a tm structure and expressed in the local time zone
time_t mktime(struct tm *timePtr);
Transfer tm to time_t
time_t time(time_t *timer);
Get current calendar time or set calendar time
struct tm* gmtime_r(time_t *timePtr, struct tm *result);
Same to gmtime (Thread Safe)
typedef int time_t;
time_t clock();
返回处理器时钟所使用的时间，需要除以 CLOCKS_PER_SEC
char* ctime(time_t *timer);
返回一个表示当地时间的字符串，当地时间是基于参数 timer
double difftime(time_t endTime, time_t fromTime);
计算两个时间的差值
struct tm* gmtime(time_t *timer);
使用 timer 的值来填充 tm 结构，并用协调世界时（UTC）也被称为格林尼治标准时间（GMT）表示
struct tm* localtime(time_t *timer);
使用 timer 的值来填充 tm 结构。timer 的值被分解为 tm 结构，并用本地时区表示
time_t mktime(struct tm *timePtr);
将tm转换为time_t
time_t time(time_t *timer);
得到当前日历时间或者设置日历时间
struct tm* gmtime_r(time_t *timePtr, struct tm *result);
等同于 gmtime (Thread Safe)