c++ - tm_wday 返回 0-6 范围之外的大整数

Question

在 c++ 中使用 tm 结构时，我得到 tm_wday 的值是大整数(例如 4199040，比预期的大得多0-6 范围:)。为什么会这样？所有其他值(例如年、月等)都是正确的。

我已经看到以前的问题，其中工作日似乎计算错误，即由于时区差异等原因，0-6 范围内的值与预期值不同。但我很困惑为什么我会得到这么大的数字？它似乎也不是内存位置(不是十六进制格式的数字)。

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


struct tm get_time(std::string timestamp_string = "2019.08.16D11:00:00"){

    struct tm tm;
    int hh, mm;
    int MM, DD, YY;
    float ss;
    const char * timestamp = timestamp_string.c_str();
    if (sscanf(timestamp,"%d.%d.%dD%d:%d:%f", &YY,&MM, &DD,&hh, &mm,&ss) != 6) std::cout<<"oops";

    tm.tm_year = YY - 1900;  // Years from 1900
    tm.tm_mon = MM - 1; // Months form January
    tm.tm_mday = DD;
    tm.tm_hour = hh;
    tm.tm_min = mm;
    tm.tm_sec = ss;
    tm.tm_isdst = 0;
    return tm;

}

int main(){
    struct tm tm = get_time("2019.08.16D11:00:00");
    std::cout<<"Year is: "<<tm.tm_year<<std::endl; //119 - is correct
    std::cout<<"Month since Jan is: "<<tm.tm_mon<<std::endl; //7 - is correct
    std::cout<<"Weekday is: "<<tm.tm_wday<<std::endl;//4199040- why is this so large?

    return 0;
}

Answer 1

环顾四周，预计在定义 tm 结构后，您运行函数 mktime() 并引用实例以更新派生值，例如 tm_wday。所以固定的main()函数应该是:

int main(){
    struct tm tm = get_time("2019.08.16D11:00:00");
    mktime(&tm); //needs to be called to update derived values such as tm_wday
    std::cout<<"Year is: "<<tm.tm_year<<std::endl; //119 - is correct
    std::cout<<"Month since Jan is: "<<tm.tm_mon<<std::endl; //7 - is correct
    std::cout<<"Weekday is: "<<tm.tm_wday<<std::endl;//shows 5 now - is correct
    return 0;
}