试图用另一个对象作为参数来构造一个对象

Question

https://imgur.com/gallery/pEw8fBs https://pastebin.com/xvWFHrTU

我的错误贴在上面..我不明白这段代码有什么问题..我正在尝试构建一本书，里面有一个日期对象。请帮忙，这也是我的第一篇文章！ :)

#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<cmath>
using namespace std;
inline void keep_window_open() { char ch; cin >> ch; }

class Date {
    int y, m, d;

public:
    Date(int d, int m, int y);
};

class Book {
    string title;
    string author;
    string isbn;
    Date date;

public:
    Book(string t, string a, string id, Date d);
};

int main() {
    Book Charlie("charlie", "gates", "333H", Date(1, 2, 3));
}

Answer 1

您的两个构造函数都已声明但未定义

class Date {
    int y, m, d;

public:
    Date(int _d, int _m, int _y) : y(_y), m(_m), d(_d) {} // definition
};

class Book {
    string title;
    string author;
    string isbn;
    Date date;

public:
    Book(string t, string a, string id, Date d)
    : title(t), author(a), isbn(id), data(d) {} // definition
};

Answer 2

如果你为Date声明一个默认构造函数，你的问题就解决了：

#include <iostream>
#include <string>

using namespace std;

class Date {
    int y, m, d;

public:
    // Default constructor which will be used in 'Book'
    Date() {}
    // Don't semicolon here, just two braces required
    Date(int d, int m, int y) {}
};

class Book {
    string title;
    string author;
    string isbn;
    // Default constructor called here
    Date date;

public:
    // You can code everything inside the braces now
    // NOTE 2: Default constructor called here
    Book(string t, string a, string id, Date d) {}
};

int main() {
    Book Charlie("charlie", "gates", "333H", Date(1, 2, 3));

    return 0;
}