- 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
- 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.
- 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.
- 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.
- 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 <stdio.h>
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:
<a href=http://www.cnblogs.com/hicjiajia/archive/2009/09/27/1574957.html>c++枚举类型_博客园</a>
