详解C++何时需要拷贝构造函数

#include <iostream>
using namespace std;
class Line
{
  public:
    string m_name;
    int m_age;
    Line();
    ~Line(); // 析构函数
    void show();
};
Line:: Line()
{
  cout << "无参构造被调用" << endl;
}
Line:: ~Line()
{
  cout << "析构函数~Line()被调用" << endl;
}
void Line:: show()
{
  cout << "姓名：" << m_name << "，年龄: " << m_age << endl;
}
int main()
{
  Line line1("张三", 18);
  Line line2 = line1;
  return 0;
}

classname (const classname &obj) 
{ 
    // 构造函数的主体 
}

#include <iostream>
using namespace std;
class Line
{
  public:
    string m_name;
    int m_age;
    Line();
    Line(string name, int age);  // 构造函数
    Line(const Line &obj);
    Line(const Line &obj, int n);
    ~Line(); // 析构函数
    void show();
};
Line:: Line()
{
  cout << "无参构造被调用" << endl;
}
Line:: Line(string name, int age)
{
  m_name = name;
  m_age = age;
  cout << "构造函数Line(string name1, int age)被调用" << endl;
}
Line:: Line(const Line &obj)
{
  cout << "拷贝构造函数被调用" << endl;
  cout << "拷贝构造 - 姓名：" << obj.m_name << "，拷贝构造 - 年龄: " << obj.m_age << endl;
  m_name = obj.m_name;
  m_age = obj.m_age;
}
Line:: ~Line()
{
  cout << "析构函数~Line()被调用" << endl;
}
// 实现成员函数
void Line:: show()
{
  cout << "姓名：" << m_name << "，年龄: " << m_age << endl;
}
int main()
{
  Line line1("张三", 18);
  Line line2 = line1;
  line2.show();
  return 0;
}