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.

Answer 2

My guess is that some other code can then check if one of (or more of) these enum values have been defined using #ifdef.