解读构造函数的调用规则、深拷贝与浅拷贝

#include<iostream>
using namespace std;
class A {
public:
	int num;
	A(int num) {
		this->num = num;
	}
};
int main()
{
	A a(5);
	A b(a);
	cout << b.num;
	return 0;
}

#include<iostream>
using namespace std;
class A {
    int num;
    int* p;
public:
    A() {
        num = 0;
        p = nullptr;
        cout << "调用无参构造" << endl;
    }
    A(int a) {
        num = a;
        p = new int[num];
        cout << "调用有参构造" << endl;
    }
    ~A() {
        if (p)delete[]p;
    }
};

int main() {
    A a(3);
    A b = a;
    return 0;
}

#include<iostream>
using namespace std;
class A {
    int num;
    int* p;
public:
    A() {
        num = 0;
        p = nullptr;
        cout << "调用无参构造" << endl;
    }
    A(int a) {
        num = a;
        p = new int[num];
        cout << "调用有参构造" << endl;
    }
    A(const A& other) {//万能引用，避免实参修改形参
        num = other.num;
        p = new int[num];//保证内存大小相同
        for (int i = 0; i < num; i++) {
            p[i] = other.p[i];//保证数据相同
        }
        cout << "调用拷贝构造" << endl;
    }
    ~A() {
        if (p)delete[]p;
        cout << "调用析构函数" << endl;
    }
};

int main() {
    A a(3);
    A b = a;
    return 0;
}

#include<iostream>
using namespace std;
class String {
    int size;
    char* p;
public:
    String() {
        p = nullptr;
        size = 0;
    }
    String(const char* p) {
        size = strlen(p);
        this->p = new char[size + 1];//\0,所以加一
        strcpy_s(this->p, size + 1, p);
    }
    ~String() {
        if (p)  delete[]p;
    }
    String(const String& other) {
        this->size = other.size;
        this->p = new char[size + 1];
        strcpy_s(this->p, size + 1,other.p);
    }
    void print() {
        cout << p<<endl;
    }
};
int main() {
    String str = "abcde";
    String str2(str);
    str2.print();
    return 0;
}