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.
The last term 'tm' will be in structure format which consists of following elements.
time_tclock_tsize_tstruct tm
| 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 |
| 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 |
More Info
The macros used in C Time Function are:
- CLOCKS_PER_SEC: The macro indicated the number of clocks taken per second by the processor.
- NULL : The null macro indicates the null pointer value which is constant.
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]
Key Points
- C Time Function use <time.h> header file.
- time_t, clock_t and size_t used to set time.