C Programming - SPLessons
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C Time Function

C Time Function

shape Description

By using C Time Function, there is a possibility of setting the date and time. C inherits the properties of functions and structures from C- library and exhibits the settings of date and time. The header file required to set date and time in C is <time.h>. Mainly, there are four C Time Function types. They are: The first three terms acts as functions and helps in showing the time and date in the form of integer. Some of the functions included in C standard libraries are given in the below table.
Functions Description
time_t time(time_t *time); Returns local time by converting time_t using pointer
char *ctime(const time_t *time); Returns local time by converting time_t using pointer
struct tm *localtime(const time_t *time); Returns to tm structure using pointer to represent local time
clock_t clock(void) Returns duration of current running program
char * asctime(const struct tm * time); Returns pointer to structure converting the data to day month date hours:minutes:seconds:year\n\0 format
struct tm * gmtime(const time_t *time); Returns pointer to structure representing the GMT time
time_t mktime(struct tm *time); Returns the exact time in the structure when pointer points it.
double difftime(time_t time2, time_t time1); Calculates the differences between time1 and time2
size_t strftime(); Returns formatted date and time
The last term 'tm' will be in structure format which consists of following elements.
Field Type Meaning Range
tm_sec int represents seconds of minutes 0-61
tm_min int represents minutes of hour 0-59
tm_hour int represents hours of day 0-23
tm_mday int represents day of month 1-31
tm_mon int represents month of year from January 0-11
tm_year int represents years since 1900
tm_wday int represents days since Sunday 0-6
tm_yday int represents days since January 1st 0-365
tm_isdst int represents hours saving day time

shape More Info

The macros used in C Time Function are:
  1. CLOCKS_PER_SEC: The macro indicated the number of clocks taken per second by the processor.
  2. NULL : The null macro indicates the null pointer value which is constant.

shape Examples

Program using clock() function [c] #include <time.h> #include <stdio.h> int main() { clock_t begin_t, stop_t, sum_t; int a; begin_t = clock(); printf("Beginning of program, begin_t = %ld\n", begin_t); printf("scanning loop, begin_t = %ld\n", begin_t); for(a=0; a< 10000000; a++) { } stop_t = clock(); printf("Ending loop, stop_t = %ld\n", stop_t); sum_t = (double)(stop_t - begin_t) / CLOCKS_PER_SEC; printf("Total time taken by CPU: %f\n", sum_t ); printf("End of the program...\n"); return(0); }[/c] Output [c] Beginning of program, begin_t = 0 scanning loop, begin_t = 0 Ending loop, stop_t = 46 Total time taken by CPU: 0.000000 End of the program...[/c] Program to find local time using asctime function [c] #include <stdio.h> #include <time.h> int main () { time_t t; struct tm *m; char buffer[50]; time( &t ); m = localtime( &t ); printf("Present local time and date is: %s", asctime(m)); return(0); }[/c] Output [c] Present local time and date is: Fri Dec 11 10:34:11 2015[/c] Program to find the execution time taken using the difference function [c] #include <stdio.h> #include <unistd.h> #include <time.h> int main () { time_t begin_t,stop_t; double difference_t; printf("Start of program\n"); time(&begin_t); printf("Wait for 3 seconds\n"); sleep(3); time(&stop_t); difference_t = difftime(stop_t, begin_t); printf("Time taken to execute = %f\n", difference_t); printf("Ending the program\n"); return(0); }[/c] Output [c] Start of program Wait for 3 seconds Time taken to execute = 3.000000 Ending the program[/c]


shape Key Points

  • C Time Function use <time.h> header file.
  • time_t, clock_t and size_t used to set time.