11深拷贝与浅拷贝

深拷贝和浅拷贝

• 没有提供任何构造函数的时候，系统默认生成构造和析构函数。
• 当需要使用拷贝构造函数是，系统默认生成拷贝构造函数，是内存拷贝。

class seqStack {
private:
	int* _pstack;
	int _size;
	int _top;

public:
	seqStack(int size) {
		_size = size;
		_pstack = new int[size];
		_top = -1;
	}
	~seqStack() {
		delete[]_pstack;
		_pstack = nullptr;
	}
};

int main() {
	seqStack s1(10);
	seqStack s2 = s1; // 默认拷贝构造，属于内存拷贝，是一种浅拷贝。
    //析构顺序与构造顺序相反，先析构s2，delete了栈空间，s1析构再次释放栈空间会报错。
}

• 对象如果占用外部资源，浅拷贝会出现问题，应转为深拷贝。
• 深拷贝：不仅做内存拷贝，还做外部资源的内容拷贝。

class seqStack {
// private:
// 	int* _pstack;
// 	int _size;
// 	int _top;

public:
	seqStack(int size) {
		_size = size;
		_pstack = new int[size];
		_top = -1;
	}
	~seqStack() {
		delete[]_pstack;
		_pstack = nullptr;
	}
    //自定义拷贝构造函数
	seqStack(const seqStack &seq) {
		_pstack = new int[seq._size];
		for (int i = 0; i <= seq._top; i++) {
			_pstack[i] = seq._pstack[i]; 
		}
		_size = seq._size;
		_top = seq._top;
	}
    //重载等号运算符
    //如果需要支持连续赋值，重载等号运算符函数应为seqStack类型，返回*this
    void operator=(const seqStack& seq) {
        if (this == &seq)  //防止自赋值
	        return;
        delete[] _pstack;
        _pstack = new int[seq._size];
        for (int i = 0; i <= seq._top; i++) {
            _pstack[i] = seq._pstack[i];
        }
        _size = seq._size;
        _top = seq._top;
    }
};

int main() {
	seqStack s1(10);
	seqStack s2(s1); //调用拷贝构造函数
    seqStack s3 = s1; //调用拷贝构造函数
    //默认的等号运算符是内存拷贝，浅拷贝
    s3 = s1；// //已经不是初始化阶段了，重载等号运算符
}