Question

I can get the system time using struct tm and time(),localtime(),asctime().but i need help about how i can set time of system using c program.

Answer 1

if you don’t want to execute a shell command you can (as you mentioned) use the settimeofday, i would start by reading the MAN page, or looking for some examples

here’s an example:

#include <sys/time.h>
#include <stdio.h>
#include <errno.h>

int main(int argc, char *argv[])
{
    struct timeval now;
    int rc;

    now.tv_sec=866208142;
    now.tv_usec=290944;

    rc=settimeofday(&now, NULL);
    if(rc==0) {
        printf("settimeofday() successful.\n");
    }
    else {
        printf("settimeofday() failed, "
        "errno = %d\n",errno);
        return -1;
    }

    return 0;
}

Shamelessly ripped From IBMs documentation, the struct timeval struct holds the number of seconds (as a long) plus the number of microseconds (as a long) from 1 January 1970, 00:00:00 UTC (Unix Epoch time). So you will need to calculate these numbers in order to set the time. you can use these helper functions, to better handle dealing with the timeval struct.