struct Point
{int _x;int _y;
};
class Date
{
public:Date(int year, int month, int day):_year(year), _month(month), _day(day){cout << "Date(int year, int month, int day)" << endl;}
private:int _year;int _month;int _day;
};
int main()
{int x1 = 1;int x2{ 2 };int array1[]{ 1, 2, 3, 4, 5 };int array2[5]{ 0 };Point p{ 1, 2 };// C++11中列表初始化也可以适用于new表达式中int* pa = new int[4] { 0 };//C++98Date d1(2022, 1, 1);//C++11Date d2{ 2022, 1, 2 };Date d3 = { 2022, 1, 3 };return 0;
}

1.2 std::initializer_list

int main()
{vector<int> v = { 1,2,3,4 };list<int> lt = { 1,2 };// 这里{"sort", "排序"}会先初始化构造一个pair对象map<string, string> dict = { {"sort", "排序"}, {"insert", "插入"} };// 使用大括号对容器赋值v = { 10, 20, 30 };return 0;
}

	//先构造再拷贝 -> 编译器优化 -> 直接构造vector<int> v1 = { 1,2,3,4,5,6,7,8,9 };//直接构造vector<int> v2{ 1,2,3,4,5,6,7,8,9 };

2. 声明

2.1 auto

template<class T1, class T2>
void F(T1 t1, T2 t2)
{decltype(t1 * t2) ret;cout << typeid(ret).name() << endl;
}
int main()
{const int x = 1;double y = 2.2;decltype(x * y) ret; // ret的类型是doubledecltype(&x) p;      // p的类型是int*cout << typeid(ret).name() << endl;cout << typeid(p).name() << endl;F(1, 'a');return 0;
}

int main() {int array[] = { 1, 2, 3, 4, 5 };// 如果要进行修改，就必须要引用for (auto& e : array)e *= 2;// 如果只是访问，可以不用引用for (auto e : array)cout << e << " " << endl;return 0;
}

3.2 范围for的使用条件

int main() {vector<int> v = { 1, 2, 3, 4, 5 };vector<int>::iterator it = v.begin();for (auto e : v)cout << e << " ";cout << endl;for (; it != v.end(); it++)cout << *it << " ";return 0;
}

5.4 禁止生成默认函数的关键字delete

void Test()
{auto f = [] {cout << "hello world" << endl; };f();
}class Date
{
public:Date(int year = 1, int month = 1, int day = 1):_year(year), _month(month), _day(day){cout << "Date(int year, int month, int day)" << endl;}Date(const Date& d):_year(d._year), _month(d._month), _day(d._day){cout << "Date(const Date& d)" << endl;}
private:int _year = 1;int _month = 1;int _day = 1;
};int main()
{auto DateLess = [](const Date* p1, const Date* p2){return p1 < p2;//偷懒直接比指针};cout << typeid(DateLess).name() << endl;// lambda对象支持拷贝构造auto copy(DateLess);// lambda对象禁掉默认构造// decltype(DateLess) xx;//运行报错//为了下面的代码运行通过，还得有比较对象DateLess，因为lambda对象不会默认构造priority_queue<Date*, vector<Date*>, decltype(DateLess)> p1(DateLess);return 0;
}

class Rate
{
public:Rate(double rate) : _rate(rate){}double operator()(double money, int year){return money * _rate * year;}
private:double _rate;
};int main()
{double rate = 0.49;Rate r1(rate);r1(10000, 2);auto r2 = [=](double monty, int year)->double {return monty * rate * year;};r2(10000, 2);auto f1 = [] {cout << "hello world" << endl; };auto f2 = [] {cout << "hello world" << endl; };f1();f2();return 0;
}

8. 包装器

8.1 function包装器

//std::function在头文件<functional>
// 类模板原型如下
template <class T> function;     // undefined
template <class Ret, class... Args>
class function<Ret(Args...)>;模板参数说明：
Ret : 被调用函数的返回类型
Args…：被调用函数的形参

        function包装器也叫作适配器。C++中的function本质是一个类模板，也是一个包装器，是对可调用对象的再封装，统一类型，可调用对象有函数指针/函数名、仿函数、lambda表达式等。   
         对于编译器而言，下面的代码模useF板会实例化3份：

template<class F, class T>
T useF(F f, T x)
{static int count = 0;cout << "count:" << ++count << endl;cout << "count:" << &count << endl;return f(x);
}double f(double i)
{return i / 2;
}struct Functor
{double operator()(double d){return d / 3;}
};int main()
{// 函数名cout << useF(f, 11.11) << endl;// 函数对象cout << useF(Functor(), 11.11) << endl;// lamber表达式cout << useF([](double d)->double { return d / 4; }, 11.11) << endl;return 0;
}

int main()
{// 调整参数的个数// 某些参数绑死function<double(double, double)> fc4 = bind(&Plus::plusd, Plus(), placeholders::_1, placeholders::_2);cout << fc4(2, 3) << endl;function<double(double)> fc5 = bind(&Plus::plusd, Plus(), placeholders::_1, 20);cout << fc5(2) << endl;return 0;
}