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;
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 times count of letters: 10 Press 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
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