How can the NTP flag be set for Linux time in C++?

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The NTP flag can be set for Linux time in C++ using the following code:

#include <sys/timex.h>

int main()
{
    struct timex tx;
    int retval;

    tx.modes = ADJ_NTP; // set the NTP flag

    retval = adjtimex(&tx); // apply the changes to the system clock

    if (retval == TIME_ERROR)
    {
        // handle error
    }

    return 0;
}

In this example, the ADJ_NTP flag is set in the modes field of the timex structure. The adjtimex function is then called to apply the changes to the system clock. If an error occurs, the application should handle it appropriately.