求某一天是星期几以及记时

c语言中的time相关函数：

#include <iostream>#include <cstdio>#include <ctime>using namespace std;void printlocaltime();int main(){  time_t rawtime;  struct tm *timeinfo;  int year, month, day;  char *weekday[] = { "Sunday", "Monday",                       "Tuesday", "Wednesday",                       "Thursday", "Friday", "Saturday"};  /* prompt user for date */  printf ("Enter year: ");   scanf ("%d", &year);   printf ("Enter month: ");   scanf ("%d", &month);    printf ("Enter day: ");   scanf ("%d", &day);  /* get current timeinfo and modify it to the user's choice */  time(&rawtime);  timeinfo = localtime(&rawtime);  timeinfo->tm_year = year - 1900;  timeinfo->tm_mon = month - 1;  timeinfo->tm_mday = day;  cout << timeinfo->tm_wday << endl;  /* call mktime: timeinfo->tm_wday will be set */  mktime(timeinfo);  cout << timeinfo->tm_wday << endl;  printf ("That day is a %s.\n", weekday[timeinfo->tm_wday]);    time_t secsnow;    time(&secsnow);    cout << ctime(&secsnow) << endl;    cout << asctime(localtime(&secsnow)) << endl;    cout << asctime(gmtime(&secsnow)) << endl;    clock_t t0 = clock();    cout << "t0 = " << t0 << endl;    printlocaltime();    long i = 10000000;    while(i--);    cout << "Hello world!" << endl;    printlocaltime();    clock_t t1 = clock();    cout << "t1 = " << t1 << endl;    clock_t t2 = t1 - t0;    cout <<"t1 - t0 = " << t2 << endl;    cout << " secs: " << ((double)t2) / CLOCKS_PER_SEC << endl;    return 0;}void printlocaltime() {    struct tm *timeptr;    time_t secsnow;    time(&secsnow);    timeptr = localtime(&secsnow);    cout << timeptr->tm_year << endl;    cout << timeptr->tm_wday << endl;    printf("The date is %d-%d-%4d\n",           (timeptr->tm_mon) +1,           (timeptr->tm_mday),           (timeptr->tm_year) + 1900);    printf("Local time is %02d:%02d:%02d\n",            timeptr->tm_hour,            timeptr->tm_min,            timeptr->tm_sec);}