auto 推导

int x = 2;//x是左值

auto&& x1 = x;// x1类型是int&

auto&& x2 = x;// x2类型是const int&

auto&& x3 = 2;// 2是右值，x3类型是 int&&

const char name[]  = "sagaga"；// name 类型是const char[7]

auto arr1 = name ；//arr1类型是 const char*

auto& arr2 = name; // arr2 类型是 const char(&) [7]

void someFunc(int, double);

auto fun1 = someFunc; // fun1 类型 void(*)(int，double)

auto& fun2 = someFunc; // fun2 类型 void(&)(int，double)

auto x = {2}; //类型为 std::initializer_list value {2}

auto x {2} ; // 与auto x = 2相同

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显示类型转换比隐式类型转换好

float a = 0.2;

int x = a *100;// 发生隐式类型转换

auto y = static_casta *100;// 发生显式类型转换