侯捷C++11课程笔记---第五，六次课

接受数量不定的参数Initializer Lists

设初值

int i;  //i has undefined value
int j{};  //j is initialized by 0
int* p;   //p has undefined value
int* q{};   //q is initialized by nullptr

不允许窄化转换

int x1(5.3);  //OK
int x2 = 5.3;  //OK
int x3{5.0};  //ERROR
int x4 = {5.3}; //ERROR

用std::initializer_list<>实现对不定参数个数的实现

void print(std::initializer_list vals)
{
	for(auto p = vals.begin();p!=vals.end();++p){
	std::cout<< *p << "n";
	}
}
print({12,5,7,9,6});

他与Variadic Templates不同之处在于后者大括号内可以是不同类型的数

Class P
{
	public:
		P(int a,int b)  //function1
		{
			cout << a << b << endl;
		}
		P(initializer_list initlist) //function2
		{
			for(auto i : initlist)
				cout << i << ' ';
		} 
}

P p(77,5);  //P(int,int), a=77 ,b=5
P q{77,5};  //P(initializer_list),values = 77 5
P r{77,5,42}; //P(initializer_list),values = 77 5 42
P s={77,5}; //P(initializer_list),values = 77 5

如果没有function2，那么q和s就会拆开同时也能成功初始化，但是r由于其中有三个数则无法初始化

{}背后是initializer_list<>,后者背后是array

initializer_list 这个东西对应的array的指针，如果复制这个东西他只是浅拷贝

min,max可以接受多个而非两个参数