《C++程序设计POJ》《WEEK4 运算符重载》《长度可变的整型数组类》《流插入运算符和流提取运算符的重载》《自加/自减运算符》...

旧城等待， 2021-11-05 12:08 179阅读 0赞

CArray a2(a1);

如果使用系统默认的复制构造函数，只会复制成员变量

a2.ptr = a1.ptr 浅拷贝 内存垃圾

赋值号 = 需要重载 浅拷贝 深拷贝

#include<iostream>
    using namespace std;
    
    class CArray
    {
        int size; //数组元素的个数
        int* ptr; //指向动态分配的数组
    public:
        CArray(int s = 0); //s代表数组元素的个数
        CArray(CArray &a); // copy constructor
        ~CArray();
        void push_back(int v);//用于在数组尾部添加一个元素v
        CArray & operator=(const CArray& a);//用于数组对象间的赋值
        
        int length() { return size; }
        int & CArray::operator[](int i)
        {
            return ptr[i];
        }
    
    }; 
    CArray::CArray(int s) :size(s)
    {
        if (s == 0)
            ptr = NULL;
        else
            ptr = new int[s];
    }
    CArray::CArray(CArray & a)
    {
        if (!a.ptr)
        {
            ptr = NULL;
            size = 0;
            return;
        }
        ptr = new int[a.size];
        memcpy(ptr, a.ptr, sizeof(int) * a.size);
        size = a.size;
    }
    CArray::~CArray()
    {
        if (ptr)
            delete[] ptr;
    }
    CArray& CArray::operator= (const CArray& a)
    {
        if (ptr == a.ptr)
            return *this;
        if (a.ptr == NULL) // 如果a里面的数组是空的
        {
            if (ptr)
                delete[] ptr;
            ptr = NULL;
            size = 0;
            return *this;
        }
        if (size < a.size)//如果原有空间够大，就不用分配新的空间
        {
            if (ptr)
                delete[] ptr;
            ptr = new int[a.size];
        }
        memcpy(ptr, a.ptr, sizeof(int)*a.size);
        size = a.size;
        return *this;
    } // CArray & CArray::operator=(const CArray & a)
    
    void CArray::push_back(int v)
    {
         //在数组尾部添加一个元素
        if (ptr)
        {
            int *tmpPtr = new int[size + 1];//重新分配空间
            memcpy(tmpPtr, ptr, sizeof(int)*size);//拷贝原数组内容
            delete[] ptr;
            ptr = tmpPtr;
        }
        else
            ptr = new int[1];
        ptr[size++] = v; // 加入新的数组元素
    }
    int main()//要编写可变长整型数组类，使之能如下使用：
    {
        CArray a;
        for (int i = 0; i < 5; ++i)
            a.push_back(i);
        CArray a2, a3;
        a2 = a;
        for (int i = 0; i < a.length(); ++i)
            cout << a2[i] << " ";
        a2 = a3;
        for (int i = 0; i < a2.length(); ++i)
            cout << a2[i] << " ";
        cout << endl;
        a[3] = 100;
        CArray a4(a);
        for (int i = 0; i < a4.length(); ++i)
            cout << a4[i] << " ";
        while (1);
        return 0;
    }

## 流插入运算符和流提取运算符的重载 ##

#if 0
    #include<iostream>
    using namespace std;
    
    
    /*假定下面程序输出为 5hello, 该补写些什么*/
    class CStudent
    {
    public:
        int nAge;
    
    };
    
    ostream& operator<<(ostream & o, const CStudent & s)
    {
        o << s.nAge;
        return o;
    }
    
    
    int main()
    {
        CStudent s;
        s.nAge = 5;
        cout <<s << "hello";
        while (1);
        return 0;
    }
    #endif
    
    /*假定c是Complex复数类的对象，现在希望写“cout << c;”，
    就能以“a+bi”的形式输出c的值，写“cin>>c;”，
    就能从键盘接受“a+bi”形式的输入，
    并且使得c.real = a,c.imag = b*/
    
    
    #include<iostream>
    #include<string>
    #include<cstdlib>
    using namespace std;
    
    class Complex
    {
        double real, imag;
    public:
        Complex(double r = 0, double i = 0) :real(r), imag(i) {};
        friend ostream & operator<<(ostream & os, const Complex & c);
        friend istream & operator>>(istream & is, Complex & c);
    };
    ostream& operator<<(ostream&os, const Complex &c)
    {
        os << c.real << "+" << c.imag << "i";
        return os;
    }
    
    istream & operator>>(istream & is, Complex & c)
    {
        string s;
        is >> s;
        int pos = s.find("+", 0);
        string sTmp = s.substr(0, pos);
        c.real = atof(sTmp.c_str());
        sTmp = s.substr(pos + 1, s.length() - pos - 2);
        c.imag = atof(sTmp.c_str());
        return is;
    
    }
    
    /*
    13.2+133i 87↙
    13.2+133i, 87
    */
    
    int main()
    {
        Complex c;
        int n;
        cin >> c >> n;
        cout << c << "," << n;
        while (1);
        return 0;
    }

自加/自减运算符的重载

自加++/自减--运算符有前置/后置之分

前置运算符作为一元运算符重载

重载为成员函数:

T &operator++();

T &operator--();

重载为全局函数：  
T &operator++(T &);  
T &operator—(T &);

\++obj, obj.operator++(), operator++(obj) 都调用上述函数

后置运算符作为二元运算符重载

多写一个参数, 具体无意义  
•重载为成员函数:  
T operator++(int);  
T operator--(int);  
•重载为全局函数:  
T operator++(T &, int);  
T operator--(T &, int);  
obj++, obj.operator++(0), operator++(obj,0) 都调用上函数

operator int( ) \{ return n; \}

int作为一个类型强制转换运算符被重载,  
Demo s;  
(int) s ; //等效于s.int();  
类型强制转换运算符重载时,  
•不能写返回值类型  
•实际上其返回值类型--类型强制转换运算符代表的类型

运算符重载的注意事项  
C++不允许定义新的运算符  
重载后运算符的含义应该符合日常习惯  
•complex\_a+ complex\_b  
•word\_a> word\_b  
•date\_b= date\_a+ n  
运算符重载不改变运算符的优先级  
以下运算符不能被重载: “.”, “.\*”, “::”, “?:”, sizeof  
重载运算符(), \[ \], ->或者赋值运算符=时, 重载函数必须声明为类的成员函数

#include<iostream>
    using namespace std;
    
    class CDemo
    {
    private:
        int n;
    public:
        CDemo(int i = 0) :n(i) {}
        CDemo & operator++(); //用于前置++形式
        CDemo operator++(int); //用于后置++形式
    
        //int作为一个类型强制转换运算符被重载,
        operator int() { return n; } // 强制类型转换，没有返回值
        friend CDemo & operator--(CDemo &); //用于前置--形式
        friend CDemo operator--(CDemo&, int); //用于后置--形式
    };
    CDemo & CDemo::operator++()
    {
        n++;
        return *this;
    }
    CDemo CDemo::operator++(int k)//后置++
    {
        CDemo tmp(*this);//记录修改前的对象
        n++;
        return tmp; // 返回修改前的对象
    
    }
    CDemo & operator--(CDemo & d)
    {
        d.n--;
        return d;
    }
    CDemo operator--(CDemo & d, int)
    {
        CDemo tmp(d);
        d.n--;
        return tmp;
    }
    
    
    
    
    
    int main()
    {
        CDemo d(5);
        cout << (d++) << ",";
        cout << d << ",";
        cout << ++d << ",";
        cout << d << endl;
        cout << (d--) << ",";
        cout << d << ",";
        cout << --d << ",";
        cout << d << endl;
    
        while (1);
        return 0;
    
    
    }

转载于:https://www.cnblogs.com/focus-z/p/11013348.html