[cpp deep dive] enum枚举类型

1. 如何声明一个枚举类型？

  enum color{red, blue, green, orange};//statement with a name of enum type
  enum {red, blue, green, orange};//or without a name

2. 如何合法使用枚举类型？

color cc1 = red;//valid
color cc01 = (color)0;//valid
int crs = red;//valid 'enum' to' int'
int crr = red + blue;//valid, enum will be converted to int and then calc.

3. 不合法的例子？

color cc2 = 0;//not valid ,'int' to 'enum'
color cc3 = 0;cc3++;//not valid, operator‘++’
color cc4 = red + blue;//not valid, 'int' to 'enum'
color cc5 = (color)(red + blue);//but this it valid.

color cc6 = (color)127;//undefined behavior but won't get an error. code will work.

4. enum的值 ?

    enum bigstep{first, sec=100, third};//first 's value = 0, sec = 100, third = 101.
    enum bigstep2{aar, aar2 = 0, aar3, aar32 = 1};//multiple enum's type have the same value.

5. enum的sizeof？

    enum size{x1,x2,x3};//sizeof(size) == 4
    enum size2{x11,x22=100000000000000LL,x33};//sizeof(size2) == 8(long long)

---

上代码片

#include 

void test_enum(){
#define PR(c) printf("id: %d\n", (c))
    enum color{r, g, b};

    enum bigstep{first, sec=100, third};//first 's value = 0, sec = 100, third = 101.
    enum bigstep2{aar, aar2 = 0, aar3, aar32 = 1};//multiple enum's type have the same value.
    enum {skip01, skip02};

    
    color c1,c2,c3;
//  c1 = 0;//error: invalid conversion from "int" to "test_enum()::color"
//  c1 = color.r;//error: expected primary-expression before "." token
//  c1 = color::r;error: ¡®color¡¯ is not a class or namespace

/*  
    OK: enum ==> int
    Not OK: int ==> enum
 */
    c1 = r;//ok
    c1 = (color)0;//ok 
    PR(c1);
    c1 = (color)5;  //undefined behavior
    PR(c1);         //just print value 5.
    c1 = (color)127;//same as above.
    PR(c1); 
    
    c2 = r;
//  c2++;// error: no ¡®operator++(int)¡¯ declared for postfix ¡®++¡¯ 
    PR(c1+c2);//valid
    int x = c1+c2;//valid
    PR(x);
//  c3 = r+b;//error: invalid conversion from ¡®int¡¯ to ¡®test_enum()::color
//  c3 = (color)r+b;//same as above due to order of compute. 
    c3 = (color)(r+b);//valid
//enum size{a,b,c};
//enum size2{a,b=1000LL,c};//error: redeclaration of ¡®b¡¯
    enum size{x1,x2,x3};
    enum size2{x11,x22=100000000000000LL,x33};

    PR(sizeof(size));
    PR(sizeof(size2));


}

int main(){
    test_enum();
    return 0;
}

6.实际例子？

further reading:
c++枚举类型_博客园