C++(11)：自定义字面量构造对象

C++11支持了可以像string str = "hello world"，从而以更直观的方式来构造对象：

#include <iostream>
using namespace std;

class Weight{
public:
	Weight(unsigned int kg):m_kg(kg){}
	unsigned int m_kg;
};

ostream& operator<<(ostream& out, const Weight& w)    //定义对象的输出函数
{
	out<<"Weight is "<<w.m_kg<< " KG"<<endl;
	return out;
}

Weight operator"" _KG(unsigned long long v)           //通过_KG定义一个字面量转换函数，返回对象
{
	return Weight(v);
}

int main(){

	Weight&& w = 20_KG;    //右值引用到字面量转换函数返回的临时对象
	cout<<w;               //输出：Weight is 20 KG
	return 0;
}