Modifying a Clock Time

Use the clock_settime() function to modify the clock time.

Important: The clock time can be modified only by a process having the WriteDeviceData capability.

The following example code demonstrates how the current clock time can be moved forward by a minute.

The following example code performs the following tasks:

1. Gets the clock id of the system clock and stores it in ClockId.

2. Gets the current time associated with ClockId using clock_gettime() and stores it in CurrTime.

3. Increments current time by a minute.

4. Sets the current time as CurrTime using clock_settime().

#include <time.h>
#include <stdio.h>
#include<errno.h>
#include<string.h>
int main()
    {
    int Ret;
    clockid_t ClockId; //Stores the clock id of the system clock
    struct timespec CurrTime; //Stores the current time
    memset(&CurrTime, 0, sizeof (struct timespec)); 
    
    //Will return the supported clock id only for the pid_t of 0.
    Ret = clock_getcpuclockid(0,&ClockId);
    if (Ret == 0)
        {
        //get the current time of ClockId.
        if(clock_gettime(ClockId, &CurrTime) == 0)
            {
            CurrTime.tv_sec+=60; //forward the time by one minute
            //set the new time for ClockId.
            Ret = clock_settime(ClockId, &CurrTime);
            if (Ret != 0)
                {
                printf("clock_settime () failed with %d\n", errno);
                }
               else
                {
                printf("clock_settime() passed\n");
                }     
            }
        else
            {
            printf("clock_gettime() failed with %d\n", errno);
            }
        }
    else
        {
        printf("clock_getcpuclockid () failed with %d\n", errno);
        }
    return Ret;
    }

The output of the above program is:

clock_settime() passed