time.h

这个头文件还是蛮奇妙的，感觉获取系统当前时间这个以后会用到，学习了一下下：

参考：

http://zhidao.baidu.com/link?url=tzhn7fKwVkAWVPZy7TrvPBuStPqXTmy3JgXY2-ieBtejERV4krkw-kmZk1F9X24w72INpe2dwaDvdmpPgUwQ7_

http://hi.baidu.com/cuixinmin_sj/item/a9619e12b594dd08e65c36a1

http://www.cplusplus.com/reference/ctime/

自己写的cpp：

#include <time.h>#include <iostream>#include <stdlib.h>  // system("pause")#include <windows.h>  // Sleep()using namespace std;const char wd[7][10] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};int main() {    struct tm *ptm;  // declare a pointer pointing to the tm(a struct to store some parameters expressing time)    time_t it;  // alias of a fundamental arithmetic type capable of representing times, as those returned by function time    time_t it_2;        /*    time_t time (time_t* timer);    Get the current calendar time as a value of type time_t.    The function returns this value,     and if the argument is not a null pointer,     it also sets this value to the object pointed by timer.    */    cout << it << endl;    cout << it_2 << endl;    it = time(NULL);    it = time(&it_2);    long int t = it;    cout << t << endl;  // time_t is a long int    cout << it << endl;  // in fact, the return value of the function time is a long int, representing the seconds from CUT(Coordinated Universal Time(1970 1 1 00:00:00))    cout << it_2 << endl;  // and the return value can be received by a return value or a parameter    cout << endl;            /*    struct tm * localtime (const time_t * timer);    Uses the value pointed by timer to fill a tm structure     with the values that represent the corresponding time,     expressed for the local timezone.    */    ptm = localtime(&it);        /*    char* asctime (const struct tm * timeptr);    Convert tm structure to string,     interprets the contents of the tm structure pointed by timeptr as a calendar time     and converts it to a C-string containing a human-readable version     of the corresponding date and time.    */    string time_file = asctime(ptm);        cout << time_file << endl;        Sleep(2000);    //system("pause");        ptm = localtime(&it);  // notice that the localtime function is just a convertor, the 'it' is still the time above, so the result is the same as above    time_file = asctime(ptm);    cout << time_file << endl;        it = time(&it);  // notice that time function is a calculator, now the 'it' is changed    ptm = localtime(&it);    time_file = asctime(ptm);    cout << "the localtime: " << time_file << endl;    ptm = gmtime(&it);    time_file = asctime(ptm);    cout << "the GMT(Greenwich mean time): " << time_file << endl;  // yes that i am in China            /*    time_t mktime (struct tm * timeptr);    mktime is a reverse of localtime, and mktime can set the unknown part of the parameter(a pointer to struct tm) according the known part    */    cout << "tell me the year, month, day, and i can tell you the weekday:" << endl;        time_t nt;    struct tm* ptw;    time(&nt);  // this 2 lines are used to get current time infomation    ptw = localtime(&nt);    cin >> ptw->tm_year >> ptw->tm_mon >> ptw->tm_mday;  // notice that if i try "use week_day_cal." to replace "ptw->", the result is wrong(a fantastic number)    ptw->tm_year -= 1900;  // it seems that without -1900, the tm_year is so large that the mktime function didnot working    ptw->tm_mon -= 1;    mktime(ptw);  // or it = mktime(ptm)    cout << ptw->tm_year + 1900 << "(year) " << ptw->tm_mon + 1 << "(month) " << ptw->tm_mday << "(day) " << "is " << wd[ptw->tm_wday] << endl;    cout << endl;    /*    double difftime (time_t end, time_t beginning);    Calculates the difference in seconds between beginning and end.    */    /*    cout << "tell me the begining time and the end time and i will tell you the difference between them: " << endl;        time_t bt;    struct tm* begin = new tm;    time(&bt);    begin = localtime(&bt);    cin >> begin->tm_year >> begin->tm_mon >> begin->tm_mday;    begin->tm_year -= 1900;    begin->tm_mon -= 1;    mktime(begin);    cout << asctime(begin) << endl;        time_t et;    struct tm* end = new tm;    time(&et);    end = localtime(&et);    cin >> end->tm_year >> end->tm_mon >> end->tm_mday;    end->tm_year -= 1900;    end->tm_mon -= 1;    mktime(end);    cout << asctime(end) << endl;    cout << "the difference(end - begin) between the 2 date are: \nyear: " << end->tm_year - begin->tm_year << "\nmonth: " << end->tm_mon - begin->tm_mon << "\nmonthday: " << end->tm_mday - begin->tm_mday << endl;    cout << difftime(mktime(begin), mktime(end)) << endl;    */        return 0;}