计算某一天是星期几

计算某一天是星期几的公式如下：

　W = (Y-1) + [(Y-1)/4] - [(Y-1)/100] + [(Y-1)/400] + D．

其中Y是年份，D是改天是Y年的第几天。具体的解释见这儿

 具体代码如下：

#include <iostream>

#include <string>

#include <sstream>

using namespace std;



const int MONTH[12]={31,28,31,30,31,30,

                     31,31,30,31,30,31,

};

const string WEEK[]={"SUN","MON","TUE","WEN","THU","FRI","SAT"};

int get_day_count(int year,int month,int day)

{

    bool isleap=((year%4==0&&year%100!=0)||(year%400==0));

    int count;

    count=0;

    if(isleap&&month>2)

        count++;

    for(int i=1;i<month;i++)

        count+=MONTH[i-1];

    count+=day;



    return count;

}

int str2int(string str)

{

    istringstream is(str);

    int n;

    is>>n;

    return n;



}

void parse(string str,int &year,int &month,int &day)

{

    size_t p1,p2;

    p1=str.find('-');

    if(p1==string::npos)

    {

        cout<<"error"<<endl;

    }

    string subs=str.substr(0,p1);

    year=str2int(subs);



    p2=str.find_last_of('-');

    if(p1==string::npos)

    {

        cout<<"error"<<endl;

    }

    subs=str.substr(p1+1,p2-p1);

    month=str2int(subs);



    subs=str.substr(p2+1);

    day=str2int(subs);

}



int main(int argc,char**argv)

{

    if(argc<2)

    {

        cout<<"usage:"<<argv[0]<<" <year>-<month>-<day>"<<endl;

        return 1;

    }

    string str(argv[1]);

    int year,month,day;

    parse(str,year,month,day);



    cout<<"year="<<year<<endl;

    cout<<"month="<<month<<endl;

    cout<<"day="<<day<<endl;

    int count;

    count=get_day_count(year,month,day);

    cout<<"count="<<count<<endl;



    int week=((year-1)+(year-1)/4-(year-1)/100+(year-1)/400+count)%7;

    

    cout<<WEEK[week]<<endl;

}

还可以利用mktime函数，参见

具体代码如下：

#include <iostream>
#include <string>
#include <sstream>
#include <ctime>
using namespace std;

const string WEEK[]={"SUN","MON","TUE","WEN","THU","FRI","SAT"};
int str2int(string str)
{
    istringstream is(str);
    int n;
    is>>n;
    return n;

}
void parse(string str,int &year,int &month,int &day)
{
    size_t p1,p2;
    p1=str.find('-');
    if(p1==string::npos)
    {
        cout<<"error"<<endl;
    }
    string subs=str.substr(0,p1);
    year=str2int(subs);

    p2=str.find_last_of('-');
    if(p1==string::npos)
    {
        cout<<"error"<<endl;
    }
    subs=str.substr(p1+1,p2-p1);
    month=str2int(subs);

    subs=str.substr(p2+1);
    day=str2int(subs);
}

int main(int argc,char**argv)
{
    if(argc<2)
    {
        cout<<"usage:"<<argv[0]<<" <year>-<month>-<day>"<<endl;
        return 1;
    }
    string str(argv[1]);
    int year,month,day;
    parse(str,year,month,day);

    cout<<"year="<<year<<endl;
    cout<<"month="<<month<<endl;
    cout<<"day="<<day<<endl;
    struct tm tm1,*tm2;
    time_t timep;
    int week;
    tm1.tm_year= year-1900;  
    tm1.tm_mon=month-1;  
    tm1.tm_mday=day;  
    tm1.tm_hour=12;  
    tm1.tm_min=0;  
    tm1.tm_sec=0;
    timep=mktime(&tm1);
    tm2=localtime(&timep);
    cout<<asctime(tm2)<<endl;

    week=(int) (tm2->tm_wday);

    cout<<WEEK[week]<<endl;
}