1. 关于赋值的疑问

什么时候需要重载赋值操作符？编译器是否提供默认的赋值操作？

编译器为每个类默认重载了赋值操作符
默认的赋值操作符仅完成 浅拷贝
当需要进行 深拷贝 时 必须重载赋值操作符
赋值操作符与拷贝构造函数有相同的存在意义

1.1 编程实验：默认赋值操作符重载

#include <iostream>
#include <string>

using namespace std;

class Test
{
    int* m_pointer;
public:
    Test()
    {
        m_pointer = NULL;
    }
    Test(int i)
    {
        m_pointer = new int(i);
    }
    Test(const Test& obj)
    {
        m_pointer = new int(*obj.m_pointer);
    }
    Test& operator = (const Test& obj)
    {
        if( this != &obj )
        {
            delete m_pointer;
            m_pointer = new int(*obj.m_pointer);
        }
        
        return *this;
    }
    void print()
    {
        cout << "m_pointer = " << hex << m_pointer << endl;
    }
    ~Test()
    {
        delete m_pointer;
    }
};

int main()
{
    Test t1 = 1;
    Test t2;
    
    t2 = t1;
    
    t1.print();
    t2.print();
    
    return 0;
}

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1.2 问题分析

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重载赋值操作符，必然需要实现深拷贝：

1.3 一般性原则

重载赋值操作符，必然需要实现 深拷贝

1.4 编程实验：数组类的优化

#include "IntArray.h"

IntArray::IntArray(int len) {    m_length = len;    }

bool IntArray::construct() {
    bool ret = true;
    m_pointer = new int[m_length];
    if (m_pointer) {
        for(int i = 0; i < m_length; i++) {
            m_pointer[i] = 0;
        }        
    } else {
        ret = false;
    }
    return ret;
}

IntArray* IntArray::NewInstance(int len) {
    IntArray* ret = new IntArray(len);
    if (!(ret && ret->construct())) {
        delete ret;
        ret = 0;
    }
    return ret;
}

int IntArray::length() {    return m_length;    }

bool IntArray::get(int index, int& value) {
    bool ret = (0 <= index) && (index < length());
    if( ret ) {
        value = m_pointer[index];
    }
    return ret;
}

bool IntArray::set(int index, int value) {
    bool ret = (0 <= index) && (index < length());
    
    if( ret ) {
        m_pointer[index] = value;
    }
    return ret;
}

int& IntArray::operator [] (int index) {
    return m_pointer[index];
}

IntArray& IntArray::operator = (const IntArray& obj) {
    if (this != &obj) {
        int* pointer = new int[obj.m_length];

        if (pointer) {
            for (int i = 0; i < obj.m_length; i++) {
                pointer[i] = obj.m_pointer[i];
            }
            m_length = obj.m_length;
            delete[] m_pointer;
            m_pointer = pointer;
        }
    }
    return *this;
}

IntArray& IntArray::self() {
    return *this;
}

IntArray::~IntArray() {    delete[] m_pointer;    }

#ifndef _INTARRAY_H_
#define _INTARRAY_H_

class IntArray {
private:
    int m_length;
    int* m_pointer;
    IntArray(int len);
    bool construct();
public:
    static IntArray* NewInstance(int len);
    int length();
    bool get(int index, int& value);
    bool set(int index, int value);
    int& operator [] (int index);
    IntArray& operator = (const IntArray& obj);
    IntArray& self();
    ~IntArray();
};
#endif

#include <iostream>
#include <string>
#include "IntArray.h"

using namespace std;

int main() {
    IntArray* a = IntArray::NewInstance(5);
    IntArray* b = IntArray::NewInstance(10);

    if( a && b ) {
        IntArray& array = a->self();
        IntArray& brray = b->self();
        
        cout << "array.length() = " << array.length() << endl;
        cout << "brray.length() = " << brray.length() << endl;
    
        array = brray;
        
        cout << "array.length() = " << array.length() << endl;
        cout << "brray.length() = " << brray.length() << endl;
    }

    delete a;
    delete b;

    return 0;
}