c - What is the purpose of a these #define within an enum?

Question

I found this code in the linux headers, /usr/include/dirent.h:

enum   
  {    
    DT_UNKNOWN = 0,
# define DT_UNKNOWN DT_UNKNOWN
    DT_FIFO = 1,
# define DT_FIFO    DT_FIFO   
    DT_CHR = 2,
# define DT_CHR     DT_CHR
    DT_DIR = 4,
# define DT_DIR     DT_DIR
    DT_BLK = 6,
# define DT_BLK     DT_BLK
    DT_REG = 8,
# define DT_REG     DT_REG
    DT_LNK = 10,
# define DT_LNK     DT_LNK
    DT_SOCK = 12,
# define DT_SOCK    DT_SOCK   
    DT_WHT = 14
# define DT_WHT     DT_WHT
  };   

What is this construct for? - why define something with an identical string, which will then compile to the int value?

Answer 1

Besides the other answers which are very good - I would go with them for the main reason - the compiler could generate warnings or errors if you try to redefine DT_UNKNOWN.