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来自：http://blog.sina.com.cn/s/blog_817a5eb6010146ad.html
作者：于超峰
在程序中，可能需要为某些整数定义一个别名，我们可以利用预处理指令#define来完成这项工作，您的代码可能是：
#define MON 1#define TUE 2#define WED 3#define THU 4#define FRI 5#define SAT 6#define SUN 7
在此，我们定义一种新的数据类型，希望它能完成同样的工作。这种新的数据类型叫枚举型。
1. 定义一种新的数据类型 - 枚举型
以下代码定义了这种新的数据类型 - 枚举型
enum DAY{ MON=1, TUE, WED, THU, FRI, SAT, SUN};
(1) 枚举型是一个集合，集合中的元素(枚举成员)是一些命名的整型常量，元素之间用逗号,隔开。
(2) DAY是一个标识符，可以看成这个集合的名字，是一个可选项，即是可有可无的项。
(3) 第一个枚举成员的默认值为整型的0，后续枚举成员的值在前一个成员上加1。
(4) 可以人为设定枚举成员的值，从而自定义某个范围内的整数。
(5) 枚举型是预处理指令#define的替代。
(6) 类型定义以分号;结束。
2. 使用枚举类型对变量进行声明
新的数据类型定义完成后，它就可以使用了。我们已经见过最基本的数据类型，如：整型int, 单精度浮点型float, 双精度浮点型double, 字符型char, 短整型short等等。用这些基本数据类型声明变量通常是这样：
char a; //变量a的类型均为字符型charchar letter;int x, y, z; //变量x,y和z的类型均为整型intint number;double m, n;double result; //变量result的类型为双精度浮点型double
既然枚举也是一种数据类型，那么它和基本数据类型一样也可以对变量进行声明。
方法一：枚举类型的定义和变量的声明分开
enum DAY{ MON=1, TUE, WED, THU, FRI, SAT, SUN};
enum DAY yesterday;enum DAY today;enum DAY tomorrow; //变量tomorrow的类型为枚举型enum DAYenum DAY good_day, bad_day; //变量good_day和bad_day的类型均为枚举型enum DAY
方法二：类型定义与变量声明同时进行：
enum //跟第一个定义不同的是，此处的标号DAY省略，这是允许的。{ saturday, sunday = 0, monday, tuesday, wednesday, thursday, friday} workday; //变量workday的类型为枚举型enum DAY
enum week { Mon=1, Tue, Wed, Thu, Fri Sat, Sun} days; //变量days的类型为枚举型enum week
enum BOOLEAN { false, true } end_flag, match_flag; //定义枚举类型并声明了两个枚举型变量
方法三：用typedef关键字将枚举类型定义成别名，并利用该别名进行变量声明：
typedef enum workday{ saturday, sunday = 0, monday, tuesday, wednesday, thursday, friday} workday; //此处的workday为枚举型enum workday的别名
workday today, tomorrow; //变量today和tomorrow的类型为枚举型workday，即enum workday
也可以：
typedef enum{ saturday, sunday = 0, monday, tuesday, wednesday, thursday, friday} workday; //此处的workday为枚举型enum workday的别名workday today, tomorrow; //变量today和tomorrow的类型为枚举型workday，即enum workday
也可以用这种方式：
typedef enum workday{ saturday, sunday = 0, monday, tuesday, wednesday, thursday, friday};workday today, tomorrow; //变量today和tomorrow的类型为枚举型workday，即enum workday
注意：同一个程序中不能定义同名的枚举类型，不同的枚举类型中也不能存在同名的命名常量。错误示例如下所示：
错误声明一：存在同名的枚举类型
typedef enum{ wednesday, thursday, friday} workday;typedef enum WEEK{ saturday, sunday = 0, monday,} workday;
错误声明二：存在同名的枚举成员
typedef enum{ wednesday, thursday, friday} workday_1;typedef enum WEEK{ wednesday, sunday = 0, monday,} workday_2;
3. 使用枚举类型的变量
3.1 对枚举型的变量赋值。
实例将枚举类型的赋值与基本数据类型的赋值进行了对比：
方法一：先声明变量，再对变量赋值
#include<</SPAN>stdio.h>enum DAY { MON=1, TUE, WED, THU, FRI, SAT, SUN };void main(){ int x, y, z; x = 10; y = 20; z = 30; enum DAY yesterday, today, tomorrow; yesterday = MON; today = TUE; tomorrow = WED; printf("%d %d %d \n", yesterday, today, tomorrow);}
方法二：声明变量的同时赋初值
#include <</SPAN>stdio.h>enum DAY { MON=1, TUE, WED, THU, FRI, SAT, SUN };void main(){ int x=10, y=20, z=30; enum DAY yesterday = MON, today = TUE, tomorrow = WED; printf("%d %d %d \n", yesterday, today, tomorrow);}
方法三：定义类型的同时声明变量，然后对变量赋值。
#include <</SPAN>stdio.h>enum DAY { MON=1, TUE, WED, THU, FRI, SAT, SUN } yesterday, today, tomorrow;int x, y, z;void main(){ x = 10; y = 20; z = 30; yesterday = MON; today = TUE; tomorrow = WED; printf("%d %d %d \n", x, y, z); //输出：10 20 30 printf("%d %d %d \n", yesterday, today, tomorrow); //输出：1 2 3}
方法四：类型定义，变量声明，赋初值同时进行。
#include <</SPAN>stdio.h>enum DAY{ MON=1, TUE, WED, THU, FRI, SAT, SUN }yesterday = MON, today = TUE, tomorrow = WED;int x = 10, y = 20, z = 30;void main(){ printf("%d %d %d \n", x, y, z); //输出：10 20 30 printf("%d %d %d \n", yesterday, today, tomorrow); //输出：1 2 3}
3.2 对枚举型的变量赋整数值时，需要进行类型转换。
#include <</SPAN>stdio.h>enum DAY { MON=1, TUE, WED, THU, FRI, SAT, SUN };void main(){ enum DAY yesterday, today, tomorrow; yesterday = TUE; today = (enum DAY) (yesterday + 1); //类型转换 tomorrow = (enum DAY) 30; //类型转换 //tomorrow = 3; //错误 printf("%d %d %d \n", yesterday, today, tomorrow); //输出：2 3 30}
3.3 使用枚举型变量
#include<</SPAN>stdio.h>enum{ BELL = '\a', BACKSPACE = '\b', HTAB = '\t', RETURN = '\r', NEWLINE = '\n', VTAB = '\v', SPACE = ' '};enum BOOLEAN { FALSE = 0, TRUE } match_flag;void main(){ int index = 0; int count_of_letter = 0; int count_of_space = 0; char str[] = "I'm Ely efod"; match_flag = FALSE; for(; str[index] != '\0'; index++) if( SPACE != str[index] ) count_of_letter++; else { match_flag = (enum BOOLEAN) 1; count_of_space++; } printf("%s %d times %c", match_flag ? "match" : "not match", count_of_space, NEWLINE); printf("count of letters: %d %c%c", count_of_letter, NEWLINE, RETURN);}
输出：match 2 timescount of letters: 10Press any key to continue
4. 枚举类型与sizeof运算符
#include<</SPAN>stdio.h>enum escapes{ BELL = '\a', BACKSPACE = '\b', HTAB = '\t', RETURN = '\r', NEWLINE = '\n', VTAB = '\v', SPACE = ' '};enum BOOLEAN { FALSE = 0, TRUE } match_flag;void main(){ printf("%d bytes \n", sizeof(enum escapes)); //4 bytes printf("%d bytes \n", sizeof(escapes)); //4 bytes printf("%d bytes \n", sizeof(enum BOOLEAN)); //4 bytes printf("%d bytes \n", sizeof(BOOLEAN)); //4 bytes printf("%d bytes \n", sizeof(match_flag)); //4 bytes printf("%d bytes \n", sizeof(SPACE)); //4 bytes printf("%d bytes \n", sizeof(NEWLINE)); //4 bytes printf("%d bytes \n", sizeof(FALSE)); //4 bytes printf("%d bytes \n", sizeof(0)); //4 bytes}
5. 综合举例
#include<</SPAN>stdio.h>enum Season //注意这里如果放在下面，后面就不能直接那样声明{ spring, summer=100, fall=96, winter};typedef enum{ Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday}Weekday;void main(){ printf("%d \n", spring); // 0 printf("%d, %c \n", summer, summer); // 100, d printf("%d \n", fall+winter); // 193 Season mySeason=winter; //就是这里，看上面的定义，也可以 enum Season mySeason if(winter==mySeason) printf("mySeason is winter \n"); // mySeason is winter int x=100; if(x==summer) printf("x is equal to summer\n"); // x is equal to summer printf("%d bytes\n", sizeof(spring)); // 4 bytes printf("sizeof Weekday is: %d \n", sizeof(Weekday)); //sizeof Weekday is: 4 Weekday today = Saturday; Weekday tomorrow; if(today == Monday) tomorrow = Tuesday; else tomorrow = (Weekday) (today + 1); //remember to convert from int to Weekday}
转载于:https://www.cnblogs.com/yfz0/p/5113802.html