c++官方文档-枚举-联合体-结构体-typedef-using

#include<iostream>
#include <new>
#include<stdio.h>
using namespace std;
/**
 * url:http://www.cplusplus.com/doc/tutorial/other_data_types/
 */
/**
 * in which all its member elements occupy the same physical space in memory.
 * The size of this type is the one of the largest member element
 */
union mytypes_t
{
    char c;
    int i;
    float f;
} mytypes;
 
/**
 * 枚举类,注意不是枚举类型,语法如下
 */
//They are declared with enum class (or enum struct) instead of just enum:
enum class Colors
    : long
    {
        black, blue, green
};
enum Color2
{
    black2, blue2, green2, white
};
 
enum class EyeColor
    : char
    {    blue, green, brown
};
 
//大神解说 https://zhuanlan.zhihu.com/p/21722362
//enum Color
//{
//    //编译出错,重新定义white
//    black, white, red
//equals this
//#define black 0
//#define white 1
//#define red 2
//};
//that is ok
enum  class Color
{
    black, white, red
};
 
//        auto white = false; // error
 
template<class T> void f(T t)
{
    using tt = T;
    tt t2;
    t2 = t;
    typedef T ttt;
    ttt t3 = t;
}
int main()
{
    /**
     * 类型别名
     * 继承自c
     * typedef existing_type new_type_name;
     * c++
     * using new_type_name=existing_type
     */
    typedef char C_1;
    C_1 c = 'A';
    using C_2 = char;
    C_2 cc = 'B';
    f();
    Colors mycolor;
    mycolor = Colors::black;
    if(mycolor == Colors::black)
    {
        mycolor = Colors::blue;
    }
    //只有一个字节长度噢
    cout << sizeof(EyeColor) << endl;
    cout << sizeof(Colors) << endl;
    cout << sizeof(Color2) << endl;
    return ;
}