C++在类之间调用static_cast转换时，需要复制构造函数

下面代码因为T2没有实现T2(T1)复制构造函数，所以编译错误

g++报错：test.cpp|23 col 25| 错误： 对‘T2::T2(T1&)’的调用没有匹配的函数

#include <vector>
#include<stdio.h>
#include <string.h>
#include<iostream>
#include <string>
using namespace std;
class T1{
	public:
	int a;
	double b;
};
class T2{
	public:
	int a;
	double b;
};
int main()
{
	T1 t1;
	t1.a = 2, t1.b = 1.5;
	T2 t2 = static_cast<T2>(t1);
	return 0;
}

类之间不能用reinterpret_cast转换，尽管定义了T2(T1&)也出错：

G++报错：test.cpp|27 col 33| 错误： 从类型‘T1’到类型‘T2’的转换无效

#include <vector>
#include<stdio.h>
#include <string.h>
#include<iostream>
#include <string>
using namespace std;
class T1{
	public:
	int a;
	double b;
};
class T2{
	public:
		T2(T1& t1)
		{
			a = t1.a;
			b = t1.b;
		}
	int a;
	double b;
};
int main()
{
	T1 t1;
	t1.a = 2, t1.b = 1.5;
	T2 t2 = reinterpret_cast<T2>(t1);
	return 0;
}