Как проще всего определить день недели при использовании time.tm_wday

const int tm_mon_num[]
{
    31,60,91,121,152,182,213,244,274,305,335
};
 
typedef struct _tm_msec{
    int tm_msec;    // milliseconds after the seconds
    int tm_sec;     // seconds after the minute - [0, 60] including leap second
    int tm_min;     // minutes after the hour - [0, 59]
    int tm_hour;    // hours since midnight - [0, 23]
    int tm_mday;    // day of the month - [1, 31]
    int tm_mon; // months since January - [0, 11]
    int tm_year;    // years since 1900
    int tm_wday;    // days since Sunday - [0, 6]
    int tm_yday;    // days since January 1 - [0, 365]
    int tm_isdst;   // daylight savings time flag
} TM_MSEC, *PTM_MSEC;
 
char* ctime_costom(DWORD time_sec, DWORD time_msec) // unix_time in sec, additional time in msec
{
    TM_MSEC time;
    char* ctime = new char[34];
    DWORD time_sec_new = time_sec;
 
    time.tm_wday = 0; time.tm_isdst = 3;time.tm_min = 0;time.tm_hour = 0;time.tm_mday = 0;time.tm_mon = 0;time.tm_yday = 0;time.tm_year = 1970;
    time_sec_new += time.tm_isdst * 3600;
 
    while (time_sec_new > 86400) // all days
    {
        time_sec_new -= 86400;
        time.tm_yday++;
    }
    while (time_sec_new > 3600) // hour
    {
        time_sec_new -= 3600;
        time.tm_hour++;;
    }
    while (time_sec_new > 60) // min
    {
        time_sec_new -= 60;
        time.tm_min++;
    }
    time.tm_sec = time_sec_new;
    while (time.tm_yday > 365) // yday
    {
        time.tm_yday -= 365;
        time.tm_year++;
    }
    time.tm_yday -= ((time.tm_year - 1970) / 4 - 1);
    if (time.tm_yday <= 31) // January
    {
        time.tm_mon = 0;
    }
    if ((time.tm_year - 1972) % 4 == 0)
    {
        for (time.tm_mon = 1; time.tm_mon != 12; time.tm_mon++)
        {
            if (time.tm_yday <= tm_mon_num[time.tm_mon] && time.tm_yday > tm_mon_num[time.tm_mon - 1])
            {
                time.tm_mday = time.tm_yday - tm_mon_num[time.tm_mon - 1];
                break;
            }
        }
    }
    else
    {
        for (time.tm_mon = 1; time.tm_mon != 12; time.tm_mon++)
        {
            if (time.tm_yday <= tm_mon_num[time.tm_mon]+1 && time.tm_yday > tm_mon_num[time.tm_mon - 1]+1)
            {
                time.tm_mday = time.tm_yday - tm_mon_num[time.tm_mon - 1]+1;
                break;
            }
        }
    }
 
    time.tm_msec = time_msec;
    if (time_msec >= 1000) {
        time.tm_sec + time_msec / 1000;
        time.tm_msec = time_msec - (time_msec / 1000) * 1000;
    }
    if (time_msec < 0) {
        time.tm_sec - 1;
        time.tm_msec = 1000 + time_msec;
    }
 
// todo add time.tm_wday;
    sprintf(ctime,"%d.%d.%d %d:%d:%d|%d", time.tm_mday, time.tm_mon+1, time.tm_year, time.tm_hour, time.tm_min, time.tm_sec, time.tm_msec);
    return ctime;
}