c++-static

static成员变量

#define _crt_secure_no_warnings
#include <iostream>

using namespace std;

class aa
{
public:
    aa(int a, int b)
    {
        m_a = a;
        m_b = b;
    }



    int getc()
    {
        m_c++;
        return m_c;
    }
    
    //静态的成员方法
    static int& getcc()
    {
        return m_c;
    }

private:
    //static修饰的静态成员变量
    static int m_c;
    int m_a;
    int m_b;
};

//静态成员变量的初始化，一定类的外边。
int aa::m_c = 100;



int main(void)
{
    aa a1(10, 20);
    aa a2(100, 200);

    cout << a1.getc() << endl;//101
    cout << a2.getc() << endl;//102

    //a1.getcc() = 200;
    aa::getcc() = 200;

    cout << a1.getc() << endl;//201
    cout << a2.getc() << endl;//202

    return 0;
}

static成员变量的练习

#define _crt_secure_no_warnings
#include <iostream>


using namespace std;

class box
{
public:
    box(int l, int w)
    {
        len = l;
        width = w;
    }

    int volume()
    {
        int v = len *width*hight;

        cout << "高度是" << hight << endl;
        cout << "体积是" <<  v << endl;

        return v;
    }

    static void changehight(int h)
    {
        hight = h;
    }
private:
    int len;
    int width;
    static int hight;

};

int box::hight = 100;



int main(void)
{
    box b1(10, 20);
    box b2(100, 200);

    b1.volume();
    b2.volume();

    box::changehight(300);

    b1.volume();
    b2.volume();


    return 0;
}

static练习求平均分

#define _crt_secure_no_warnings
#include <iostream>


using namespace std;

class box
{
public:
    box(int l, int w)
    {
        len = l;
        width = w;
    }

    int volume()
    {
        int v = len *width*hight;

        cout << "高度是" << hight << endl;
        cout << "体积是" <<  v << endl;

        return v;
    }

    static void changehight(int h)
    {
        hight = h;
    }
private:
    int len;
    int width;
    static int hight;

};

int box::hight = 100;



int main(void)
{
    box b1(10, 20);
    box b2(100, 200);

    b1.volume();
    b2.volume();

    box::changehight(300);

    b1.volume();
    b2.volume();


    return 0;
}

static成员变量占用大小

static不占实际空间

#include    <iostream>
using namespace std;

class   c1
{
public:
    int i;      //4
    int j;      //4
    int k;      //4
};  //12

class   c2
{
public:
    int i;
    int j;
    int k;
    static int  m;                                                                          //4
public:
    int getk()  const   { return    k; }        //4
    void    setk(int    val)    { k = val; }    //4
};


struct  s1
{
    int i;
    int j;
    int k;
};  //12

struct  s2
{
    int i;
    int j;
    int k;
    static int  m;
};  //12?

int main()
{
    cout << "c1 :   " << sizeof(c1) << endl;
    cout << "c1 :   " << sizeof(c2) << endl;

    c2 c1, c2;

    //c1.getk();  //为什么会return c1.k 
    //c2.getk(); // 为什么会return c2.k

    cout << " ----- " << endl;

    cout << "c1 :   " << sizeof(s1) << endl;
    cout << "c1 :   " << sizeof(s2) << endl;

    return 0;
}

static仓库进出练习

#define _crt_secure_no_warnings
#include <iostream>


using namespace std;


class goods
{
public:
    goods()
    {
        weight = 0;
        next = null;
        cout << "创建了一个重量为" << weight << "的货物" << endl;
    }

    goods(int w) {
        //需要创建一个w的货物，并且仓库加上这个重量
        weight = w;
        next = null;
        total_weight += w;
        cout << "创建了一个重量为" << weight << "的货物" << endl;
    }

    ~goods() {
        //仓库减少这个货物的重量
        cout << "删除了一箱重量是" << weight << "的货物" << endl;
        total_weight -= weight;
    }


    static int get_total_weight()
    {
        return total_weight;
    }

    goods *next;
private:
    int weight;//重量
    static int total_weight;//仓库的总重量
};

int goods::total_weight = 0;


void buy(goods * &head, int w)
{
    //创建一个货物 重量是w
    goods *new_goods = new goods(w);

    if (head == null) {
        head = new_goods;
    }
    else {
        new_goods->next = head;
        head = new_goods;
    }

}

void sale(goods * &head)
{
    if (head == null) {
        cout << "仓库中已经没有货物了。。" << endl;
        return;
    }

    goods *temp = head;
    head = head->next;

    delete temp;
    cout << "saled." << endl;
}



int main(void)
{
    int choice = 0;
    goods *head = null;
    int w;

    do {
        cout << "1 进货" << endl;
        cout << "2 出货" << endl;
        cout << "0 退出" << endl;

        cin >> choice;
        switch (choice)
        {
        case 1:
            //进货
            cout << "请输出要创建货物的重量" << endl;
            cin >> w;
            buy(head, w);
            break;
        case 2:
            //出货
            sale(head);
            break;
        case 0:
            //退出
            return 0;
        default:
            break;
        }

        cout << "当前仓库的总重量是"<<goods::get_total_weight() << endl;

    } while (1);
    
    return 0;
}