Get current current day time in fractional days format.

fday.c

#include <stdio.h>
#include <time.h>

int main(int argc, char** argv){
    //Get current time
    time_t now = time(0);
    struct tm* now_tm = localtime(&now);

    //Get midnight today
    struct tm today;
    today.tm_sec = 0;
    today.tm_min = 0;
    today.tm_hour = 0;
    today.tm_year = now_tm->tm_year;
    today.tm_mon = now_tm->tm_mon;
    today.tm_mday = now_tm->tm_mday;

    //Get seconds since midnight today.
    double seconds = difftime(now, mktime(&today));

    //Get fractional time.
    double fraction = seconds/(60*60*24);
    printf("%f\n", fraction);
}