Time. In ANSI standard library H header file

Need to know something about “ Time ” and “ date ” The concept of , There are mainly the following ： 

Coordinated Universal Time（UTC）： Coordinated universal time , Also known as world standard time , It's known as Greenwich mean time （Greenwich Mean Time,GMT）. such as , Time and in mainland China UTC The time difference is +8, That is to say UTC+8. The United States is UTC-5. 

Calendar Time： Calendar time , Yes, it is “ The number of seconds elapsed from a standard point in time to this point ” To represent the time of . This standard time point will be different for different compilers , But for a compilation system say , This standard time point is constant , The calendar time corresponding to the time in the compilation system is measured by the standard time point , So it can be said that the calendar time is “ Relative time ”, But no matter which time zone you are in , At the same time, for the same standard point in time , The calendar time is the same . 

epoch： Point in time . The time point is in the standard C/C++ Is an integer , It uses the number of seconds between the time at this time and the standard time point （ Calendar time ） To express . 

clock tick： Clock timing unit （ Instead of calling it clock ticks ）, The duration of a clock unit is determined by CPU The control of the . One clock tick No CPU One clock cycle of , It is C/C++ A basic unit of time for . 

We can use ANSI In the standard library time.h The header file . The method used for the time and date defined in this header file , Whether in structural definition , Or naming , Both have obvious C Language style .