enum 随笔

工作中的代码常看到在一个类里面定义一个 enum , 而只用这个 enum,  也许没有把它放到类中的必要, 但是不放到类中, 每一个枚举量在namespace就是直接可见的, 也不太好

写了个测试小程序

注意到,  enum和int是一个size,  4 bytes.   enum中的枚举量(常量), 在它所在的namespace中直接可见,   class也是定义了一个namespace

20,21行两种转换方式, 不转换是编译不过的

22,23 两种定义枚举变量的方式

  1 #include <iostream>
  2 using namespace std;
  3 
  4 enum Type {
  5         A = 0,
  6         B ,
  7         C = 6
  8 };
  9 
 10 class WY {
 11     public:  // private by default
 12         enum Love {
 13         SOCCER,
 14         GIRL = 5,
 15         CODING = 9
 16     };
 17 };  // ; needed after class definition
 18 
 19 int main (){
 20     cout<<"the size of enum Type:" << sizeof(Type) << endl
 21         <<"the size of int:" << sizeof(int) << endl;
 22     Type type = static_cast<Type>(5);
 23     enum Type type2 = Type(7);  //两种定义方式, 下面这种好
 24 //  cout << "Type::A = " << Type::A <<endl;     //error, Type is not a class or a namespace 
 25     cout << "A = " << A << endl;
 26     cout << "B = " << B << endl;
 27     cout << "C = " << C << endl;
 28     cout << "type = " << type << endl;
 29     cout << "type2 = " << type2 << endl;
 30 //  A++;  //error
 31 //  type++;  //error
 32 
 33     int t = C * 2;
 34     cout << "t = " << t << endl;
 35 
 36     t = WY::GIRL;
 37     cout << "again t = " << t <<endl;
 38     return 0;
 39 }
                                                                                                                                    

编译结果

the size of enum Type:4
the size of int:4
A = 0
B = 1
C = 6
type = 5
type2 = 7
t = 12
again t = 5