day-11 代码

• 数量不定的参数模板

  void print()
  {
  }
  //...就是pack(包)
  template<typename T, typename... Types>
  //print(7.5,"hello",bitset<16>(377),42);  ...部分就是{"hello",bitset<16>(377),42}
  void print(const T& firstArg, const Types&... args)
  {
  	//sizeof...(args)是args参数的个数
  	cout << sizeof...(args) << " ";
  	cout << firstArg << endl;
  	print(args...);
  }
  
  /*template<typename... Types>
  void print(const Types&... args)
  {
  	cout << sizeof...(args) << " ";
  }*/
  
  int main()
  {
  
  	print(7.5, "hello", (377), 42);
  
  
  	cout << endl;
  	return 0;
  }

• lambda函数

  int a = 123;
  	auto f = [a] { cout << a << endl; };
  	f(); // 输出：123
  
  	//或通过“函数体”后面的‘()’传入参数
  	auto x = [](int a) { cout << a << endl; };
  	x(123);
  	cout << endl;

• initializer_list

  void print(initializer_list<int> vals)
  {
  	for (auto p = vals.begin(); p != vals.end(); p++)
  	{
  		cout << *p << "\n";
  	}
  	cout << endl;
  }
  
  int main()
  {
  	print({ 10,5,2,29,30,55,2 });
  
  	cout << endl;
  	return 0;
  }

• 初始化列表和普通构造函数

  class P
  {
  public:
  	P(int a, int b)
  	{
  		cout << "P(int,int), a=" << a << ",b=" << b << endl;
  	}
  	P(initializer_list<int>initial)
  	{
  		cout << "P(initalizer_list<int>,values=";
  		for (auto i : initial)
  		{
  			cout << i << " ";
  		}
  		cout << endl;
  	}
  
  
  };
  
  
  int main()
  {
  	P p(55, 7);
  	P q{ 9,20 };
  	P r{ 4, 29, 66 };
  	P s = { 99, 10 };
  
  	cout << endl;
  	return 0;
  }
  
  /* cout：
  P(int,int), a=55,b=7
  P(initalizer_list<int>,values=9 20
  P(initalizer_list<int>,values=4 29 66
  P(initalizer_list<int>,values=99 10
  */

• explicit

  class P
  {
  public:
  	P(int a, int b)
  	{
  		cout << "P(int a, int b)\n";
  	}
  	P(initializer_list<int>)
  	{
  		cout << "P(initializer_list<int>)\n";
  	}
  	explicit P(int a, int b, int c)
  	{
  		cout << "explicit P(int a, int b, int c)\n";
  	}
  };
  
  void fp(const P&) { };
  
  
  int main()
  {
  	P p1{ 77, 5 };
  	P P2{ 77, 5 };
  	P p3{ 77, 5, 42 };
  	P p4 = { 77, 5 };
  	P p5 = { 77, 5, 42 };
  	P p6(77, 5, 42);
  	cout << endl;
  
  	fp({ 47, 11 });
  	fp({ 47,11,3 });
  	fp(P{ 47,11 });
  	fp(P{ 47,11,3 });
  	cout << endl;
  
  
  	P p11{ 77, 4, 42, 500 };
  	P p12 = { 77,5,42,500 };
  	P p13{ 10 };
  
  	cout << endl;
  	return 0;
  }
  /* cout
  P(initializer_list<int>)
  P(initializer_list<int>)
  P(initializer_list<int>)
  P(initializer_list<int>)
  P(initializer_list<int>)
  explicit P(int a, int b, int c)
  
  P(initializer_list<int>)
  P(initializer_list<int>)
  P(initializer_list<int>)
  P(initializer_list<int>)
  
  P(initializer_list<int>)
  P(initializer_list<int>)
  P(initializer_list<int>)
  */

• 
• for循环的容器表达式

  	vector<double> vec{ 2, 3, 4, 5, 6, 7, 8};
  	for (auto elem : vec) {
  		cout << elem << endl;
  	}
  	cout << endl;
  	for (auto& elem : vec)
  	{
  		elem *= 3;
  	}
  	for (auto elem : vec) {
  		cout << elem << endl;
  	}
  
  /*output
  2
  3
  4
  5
  6
  7
  8
  
  6
  9
  12
  15
  18
  21
  24
  */