在 C 中声明 typedef 枚举的正确方法？

Question

像这样在 C 中声明 enum 是正确的方法吗:

typedef enum
 {
     K4ABT_SENSOR_ORIENTATION_DEFAULT = 0,        
     K4ABT_SENSOR_ORIENTATION_CLOCKWISE90,        
     K4ABT_SENSOR_ORIENTATION_COUNTERCLOCKWISE90, 
     K4ABT_SENSOR_ORIENTATION_FLIP180,            
 } k4abt_sensor_orientation_t;

不应该是:

typedef enum
 {
     K4ABT_SENSOR_ORIENTATION_DEFAULT = 0,        
     K4ABT_SENSOR_ORIENTATION_CLOCKWISE90 = 1,        
     K4ABT_SENSOR_ORIENTATION_COUNTERCLOCKWISE90 = 2, 
     K4ABT_SENSOR_ORIENTATION_FLIP180 = 3,            
 } k4abt_sensor_orientation_t;

?

Answer 1

来自 C 标准(6.7.2.2 枚举说明符)

3 The identifiers in an enumerator list are declared as constants thathave type int and may appear wherever such are permitted.127) Anenumerator with = defines its enumeration constant as the value of theconstant expression. If the first enumerator has no =, the value ofits enumeration constant is 0. Each subsequent enumerator with no =defines its enumeration constant as the value of the constantexpression obtained by adding 1 to the value of the previousenumeration constant. (The use of enumerators with = may produceenumeration constants with values that duplicate other values in thesame enumeration.) The enumerators of an enumeration are also known asits members.

例如所有这些声明都是等价的

typedef enum
 {
     K4ABT_SENSOR_ORIENTATION_DEFAULT,        
     K4ABT_SENSOR_ORIENTATION_CLOCKWISE90,        
     K4ABT_SENSOR_ORIENTATION_COUNTERCLOCKWISE90, 
     K4ABT_SENSOR_ORIENTATION_FLIP180,            
 } k4abt_sensor_orientation_t;

typedef enum
 {
     K4ABT_SENSOR_ORIENTATION_DEFAULT = 0,        
     K4ABT_SENSOR_ORIENTATION_CLOCKWISE90,        
     K4ABT_SENSOR_ORIENTATION_COUNTERCLOCKWISE90, 
     K4ABT_SENSOR_ORIENTATION_FLIP180,            
 } k4abt_sensor_orientation_t;

typedef enum
 {
     K4ABT_SENSOR_ORIENTATION_DEFAULT,        
     K4ABT_SENSOR_ORIENTATION_CLOCKWISE90 = 1,        
     K4ABT_SENSOR_ORIENTATION_COUNTERCLOCKWISE90, 
     K4ABT_SENSOR_ORIENTATION_FLIP180,            
 } k4abt_sensor_orientation_t;

typedef enum
 {
     K4ABT_SENSOR_ORIENTATION_DEFAULT,        
     K4ABT_SENSOR_ORIENTATION_CLOCKWISE90,        
     K4ABT_SENSOR_ORIENTATION_COUNTERCLOCKWISE90 = 2, 
     K4ABT_SENSOR_ORIENTATION_FLIP180,            
 } k4abt_sensor_orientation_t;

typedef enum
 {
     K4ABT_SENSOR_ORIENTATION_DEFAULT,        
     K4ABT_SENSOR_ORIENTATION_CLOCKWISE90,        
     K4ABT_SENSOR_ORIENTATION_COUNTERCLOCKWISE90, 
     K4ABT_SENSOR_ORIENTATION_FLIP180 = 3,            
 } k4abt_sensor_orientation_t;

typedef enum
 {
     K4ABT_SENSOR_ORIENTATION_DEFAULT = 0,        
     K4ABT_SENSOR_ORIENTATION_CLOCKWISE90 = 1,        
     K4ABT_SENSOR_ORIENTATION_COUNTERCLOCKWISE90 = 2, 
     K4ABT_SENSOR_ORIENTATION_FLIP180 = 3,            
 } k4abt_sensor_orientation_t;

typedef enum
 {
     K4ABT_SENSOR_ORIENTATION_FLIP180 = 3,            
     K4ABT_SENSOR_ORIENTATION_COUNTERCLOCKWISE90 = 2, 
     K4ABT_SENSOR_ORIENTATION_CLOCKWISE90 = 1,        
     K4ABT_SENSOR_ORIENTATION_DEFAULT = 0,        
 } k4abt_sensor_orientation_t;

但是为了提高可读性，我更喜欢这个声明

typedef enum
 {
     K4ABT_SENSOR_ORIENTATION_DEFAULT = 0,        
     K4ABT_SENSOR_ORIENTATION_CLOCKWISE90 = 1,        
     K4ABT_SENSOR_ORIENTATION_COUNTERCLOCKWISE90 = 2, 
     K4ABT_SENSOR_ORIENTATION_FLIP180 = 3,            
 } k4abt_sensor_orientation_t;

尤其是当枚举包含许多枚举器时。