Question

我正在尝试为格里高利日期计算器创建一个复制构造函数。

myDate.cpp (minimal)

#include "stdafx.h"
#include "myDate.h"

        int month = 0, day = 0, year = 0;

        myDate::myDate()
        {
            month = 5; day = 11; year = 1959; // Default date
        }

        myDate::myDate(int M, int D, int Y)
        {
            month = M; day = D; year = Y;
        }

        myDate::myDate(const myDate& D)
        {
            month = D.month;
            day = D.day;
            year = D.year;
        }

我得到的错误'月'不是'myDate'的成员（白天和年份相同），而“myDate”类没有成员“月”（白天和年份相同）。创建复制构造函数的正确语法是什么？这是我见过广泛使用的语法。非常感谢任何帮助！

以下是完整的标题：

myDate.h

#ifndef MYDATE_H
#define MYDATE_H

#include <string>
using namespace std;

class myDate
{
    myDate();
    myDate(int M, int D, int Y);
    myDate(const myDate &D);
    string dayName();
    int getMonth();
    int getDay();
    int getYear();
    int Greg2Julian(int M, int D, int Y);
    void Julian2Greg(int JD, int& J, int& K, int& I);
    void display();
    void increaseDate(int N);
    void decreaseDate(int N);
    int daysBetween(myDate D);
    int dayOfYear();

};
#endif

和完整的cpp：

myDate.cpp

#include "stdafx.h"
#include <iostream>
#include <string>
#include "myDate.h"
using namespace std;


        int month = 0, day = 0, year = 0;
        string months[12] = { "January", "February", "March", "April", "May", "June", "July", "September", "October", "November", "December" };
        int dayCount[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
        string weekdays[7] = { "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday", "Monday" };

        myDate::myDate()
        {
            month = 5, day = 11, year = 1959; // Default date
        }

        myDate::myDate(int M, int D, int Y)
        {
            int nM = M; int nD = D; int nY = Y;
            int JD = Greg2Julian(M, D, Y);
            Julian2Greg(JD, nM, nD, nY);
            if (nM == M && nD == D && nY == Y)
                month = M, day = D, year = Y;
            else
                month = 5, day = 11, year = 1959;
        }

        myDate::myDate(const myDate& D)
        {
            month = D.month;
            day = D.day;
            year = D.year;
        }

        int myDate::getMonth()
        {
            return month;
        }

        int myDate::getDay()
        {
            return day;
        }

        int myDate::getYear()
        {
            return year;
        }

        int myDate::Greg2Julian(int M, int D, int Y)
        {
            return D - 32075 + 1461 * (Y + 4800 + (M - 14) / 12) / 4 + 367 * (M - 2 - (M - 14) / 12 * 12) / 12 - 3 * ((Y + 4900 + (M - 14) / 12) / 100) / 4;
        }

        void myDate::Julian2Greg(int JD, int& J, int& K, int& I) //use reference variables
        {
            int L = JD + 68569;
            int N = 4 * L / 146097;
            L = L - (146097 * N + 3) / 4;
            I = 4000 * (L + 1) / 1461001;
            L = L - 1461 * I / 4 + 31;
            J = 80 * L / 2447;
            K = L - 2447 * J / 80;
            L = J / 11;
            J = J + 2 - 12 * L;
            I = 100 * (N - 49) + I + L;
        }

        void myDate::display()
        {
            cout << months[month-1] << " " << day << ", " << year;
        }

        void myDate::increaseDate(int N)
        {
            Julian2Greg(Greg2Julian(month, day, year) + N, month, day, year);
        }

        void myDate::decreaseDate(int N)
        {
            Julian2Greg(Greg2Julian(month, day, year) - N, month, day, year);
        }

        int myDate::daysBetween(myDate D)
        {
            return Greg2Julian(D.getMonth(), D.getDay(), D.getYear()) - Greg2Julian(month, day, year);
        }

        int myDate::dayOfYear()
        {
            int sum = 0;
            for (int i = 0; i < month; i++)
            {
                if (month > i + 1)
                    sum += dayCount[i];
                else
                    sum += day;
            }
            return sum;
        }

        string myDate::dayName()
        {
            int dayNum = Greg2Julian(month, day, year) %7;
            return weekdays[dayNum];
        }

Answer 1

由于变量是全局变量，myDate类的所有实例（在某种程度上）将共享相同的变量。如果您为一个对象更改month，则会为所有对象更改它。

这就是为什么你会遇到错误的原因D.month，因为month类中没有成员myDate。

如果您希望这三个人成为班级的实际成员，那么您需要做类似

的事情

class myDate
{
    int month, day, year;

public:
    // The rest of the class and its member functions...
};

然后从源文件中删除全局变量。

最后，我建议你从一开始就获得a couple of good books to read。

复制构造函数语法错误：myclass没有成员mymember

1 个答案: