enum与typedef enum的用法-蒲公英云

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。

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。

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char
char letter;
int x,
y,
z; //变量x,y和z的类型均为整型int
int 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 DAY
enum 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;

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<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 <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 <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 <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 <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<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 times
count of letters: 10
Press any key to continue

枚举类型与sizeof运算符

#include<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

}

综合举例

#include<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