[c++] Which one: structure or class

有了类，还要结构体做什么？

---

一、结构体de构造函数

构造函数在结构体内元素比较多的时候会使得代码精炼，因为可以不需要临时变量就可以初始化一个结构体，而且整体代码更简洁。这就是构造函数的精妙之处。

结构体中，也可以设置一些默认值，比如年假什么的．

#include<stdio.h>

struct Point{
    int x, y;
    Point(){}    //　用以不经初始化地定义pt[10]
    Point(int _x, int _y): x(_x), y(_y) {}     //　用以提供x和y的初始化
}pt[10];


int main(){
    int num = 0;

    for(int i = 1; i <= 3; i++){
        for(int j = 1; j <= 3; j++){
            pt[num++] = Point(i, j);      //　<-- 直接使用构造函数，看上去干净了许多
        }
    }

    for(int i = 0; i < num; i++){
        printf("%d,%d\n", pt[i].x, pt[i].y);
    }

    return 0;
}

 

 

二、结构体作为参数

与类对象一样，结构体变量也可以通过值、引用和常量引用传递给函数。默认情况下，它们使用值传递．

加上const，常量引用传入即可．

#include <iostream>
#include <iomanip>
#include <string>

using namespace std;

struct Invltem// Holds data for an inventory item
{
    int partNum; // Part number
    string description; // Item description
    int onHand; // Units on hand
    double price; // Unit price
};

// Function prototypes
void getltemData(InvItem &) ;
void showItem(const InvItem &);

int main()
{
    InvItem part; // Define an Invltem structure variable.
    getItemData(part);
    showItem(part);

    return 0;
}

void getItemData(InvItem &item)
{
    cout << "Enter the part number: ";
    cin >> item.partNum;
    cout << "Enter the part description: ";
    cin.get();
    getline (cin, item.description);
    cout << "Enter the quantity on hand: ";
    cin >> item.onHand;
    cout << "Enter the unit price: ";
    cin >> item.price;
}

void showItem(const InvItem &item)
{
    cout << fixed << showpoint << setprecision(2) << endl;
    cout << "Part Number : " << item.partNum << endl;
    cout << "Description : " << item.description << endl;
    cout << "Units On Hand : " << item.onHand << endl;
    cout << "Price    : $" << item.price << endl;
}

 

 

三、结构体de继承

Bear in mind you can use virtual inheritance with structs. They are THAT identical.

struct能继承吗？ 能！！

struct能实现多态吗？ 能！！！

 

• 不使用虚继承

struct Animal {
    virtual ~Animal() = default;
    virtual void Eat() {}
};

struct Mammal: Animal {
    virtual void Breathe() {}
};

struct WingedAnimal: Animal {
    virtual void Flap() {}
};

// A bat is a winged mammal
struct Bat: Mammal, WingedAnimal {};

Bat bat;

强制类型转换，告诉编译器，访问＂祖父类＂是通过的哪个＂父类＂.

Bat b;

Animal& mammal = static_cast<Mammal&>(b); 
Animal& winged = static_cast<WingedAnimal&>(b);

 

• 使用虚继承

struct Animal {
    virtual ~Animal() = default;
    virtual void Eat() {}
};

// Two classes virtually inheriting Animal:
struct Mammal: virtual Animal {
    virtual void Breathe() {}
};

struct WingedAnimal: virtual Animal {
    virtual void Flap() {}
};

// A bat is still a winged mammal
struct Bat: Mammal, WingedAnimal {};

 

End.