typedef enum与enum的用法-CFANZ编程社区

typedef enum {
	RESET = 0, 
	SET = !RESET
} FlagStatus, ITStatus;

这句话意思就是给enum {RESET = 0, SET = !RESET}起了别名：FlagStatus和ITStatus

在这之后出现的 FlagStatus和ITStatus 可以视为 enum {RESET = 0, SET = !RESET}

这样做目的是为了节约代码，提升可阅读性，同时也易于维护~

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称，是一个可选项，即不写也可以。
（3）第一个枚举成员的值如不赋予，则默认值为整型的0，后续枚举成员的值在前一个成员上加上1。即上述代码中的TUE值为2。
（4）可以认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

常见的基本数据类型有
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。这些基本数据类型声明变量通常是这样的：

char a; // 变量a的类型均为字符型char
int x,y,z;//变量x，y，z的类型均为整型int
double m,n;//变量resul的类型为双精度浮点型double

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 today;//变量today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  //此处省略DAY
{
	MON = 1,
	TUE,
	WED,
	THU,
	FRI,
	SAT,
	SUN
}workday;//变量workday的类型为枚举型enum DAY

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
{
	MON = 1,
	TUE,
	WED,
	THU,
	FRI,
	SAT,
	SUN
}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

也可以这样表示

typedef enum 
{
	MON = 1,
	TUE,
	WED,
	THU,
	FRI,
	SAT,
	SUN
}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

或者这种表达方式

typedef enum workday
{
	MON = 1,
	TUE,
	WED,
	THU,
	FRI,
	SAT,
	SUN
}; 

workday today, tomorrow; //变量today和tomorrow的类型为枚举型workday,即enum workday

错误声明

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<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 <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 <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 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<</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
}

本文借鉴CSDN博主「ppaiml」的文章，原文链接为：https://blog.csdn.net/yuantuo3887/article/details/79211313