复制构造函数的调用

#include <iostream>
using namespace std;

class Test
{
public:
  Test(int n = 1)
  {
    val = n;
    cout << "Con." << endl;
  }

  Test(const Test& t)
  {
    val = t.val;
    cout << "Copy con." << endl;
  }

  Test& operator=(Test& t)
  {
    val = t.val;
    cout << "Assignment." << endl;
    return *this;
  }

private:
  int val;
};

void func1(Test t)
{
}

Test func2()
{
  Test t;
  return t;
}

void main()
{
  Test t1(1);

  Test t2 = t1; // ①

  Test t3;
  t3 = t1;

  func1(t2); // ②

  t3 = func2(); // ③
}

运行结果：
Con.
Copy con.[①创建并初始化对象t2，调用复制构造函数]
Con.
Assignment.
Copy con.[②实参以传值方式初始化形参，调用复制构造函数]
Con.
Copy con.[③调用复制构造函数简历临时对象，作为函数返回值]
Assignment.