36-經典問題解析三

36-經典問題解析三

關於賦值的疑問

【問題】什麼時候需要重載賦值操作符？編譯器是否提供默認的賦值操作？

• 編譯器爲每個類默認重載了賦值操作符
• 默認的賦值操作符僅完成淺拷貝
• 當需要進行深拷貝時必須重載賦值操作符
• 賦值操作符與拷貝構造函數有相同的存在意義

【範例代碼】默認賦值操作符重載

#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(int argc, const char* argv[]) {
    Test t1 = 1;
    Test t2;

    t2 = t1;

    t1.print();
    t2.print();

    return 0;
}