Why use enum when #define is just as efficient?

Question

So an enum works like this:

enum {
  false,
  true
}

which is equivalent to

int false = 0
int true = 1

Why wouldn't I substitute enum with #define?

#define FALSE 0
#define TRUE 1

To me, it seems like they are interchangeable. I'm aware that #define is able to handle arguments, hence operates in an entirely different way than enum. What exactly are the main uses of enum when we have #define in this case?

If I were to guess, as the #define is a preprocessor feature, enum would have some runtime advantages. How far off am I?

Thanks in advance.

see http://stackoverflow.com/questions/136946/difference-between-enum-and-define-statements — SirDarius, Mar 09 '11 at 08:56
Odd, that one didn't appear within my search results. Thanks! — userenum, Mar 09 '11 at 09:02
It is not equivalent to `int false = 0` nor to `int const false = 0` (which would be more appropriate). `int` variables would have an address, you could then do `&false`, which you can't for an `enum`. — Jens Gustedt, Mar 09 '11 at 10:40
Note that [SO 136946](http://stackoverflow.com/q/136946/) is tagged with both C++ and C. Nominally, it is not as good a choice of duplicate as SO 1674032 which is for C only, but I could be persuaded otherwise. — Jonathan Leffler, Nov 30 '15 at 23:47
It's funny that I found this question whilst wondering on exact the opposite: why are C programmers using `#defines`s instead of `enum`s. — Hi-Angel, Nov 17 '18 at 09:08

score 33 · Accepted Answer · edited May 26 '20 at 08:23

33

The advantages of enum show up when you have a long list of things you want to map into numbers, and you want to be able to insert something in the middle of that list. For example, you have:

pears 0
apples 1
oranges 2
grapes 3
peaches 4
apricots 5

Now you want to put tangerines after oranges. With #defines, you'd have to redefine the numbers of grapes, peaches, and apricots. Using enum, it would happen automatically. Yes, this is a contrived example, but hopefully it gives you the idea.

edited May 26 '20 at 08:23

Roberto Caboni

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answered Mar 09 '11 at 09:03

jcomeau_ictx

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1

Yes, I see the difference now. Thanks! – userenum Mar 09 '11 at 09:06
5

This is a good answer. **But assumes** the reader (who could be any NOOB) knows that she can declare an `enum` with `pears 0` and NOT number the rest. – gideon Nov 25 '14 at 03:04

score 18 · Answer 2 · answered Mar 09 '11 at 08:51

18

I find it useful for debugging in an environment such as gdb since enum values are handled at compile time (where #define is a preprocessor macro) and thus available for introspection.

answered Mar 09 '11 at 08:51

mduvall

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score 5 · Answer 3 · edited May 26 '20 at 08:24

5

Although your question is tagged as C, there is a big advantage when writing in C++, you can place enum:s inside classes or namespaces.

This way you could refer to your constants like SpaceshipClass::galaxy.

edited May 26 '20 at 08:24

Roberto Caboni

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answered Mar 09 '11 at 09:58

Lindydancer

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score 0 · Answer 4 · answered Mar 09 '11 at 09:32

0

enum is an integer constant. so, there would be a type check during compilation process.

answered Mar 09 '11 at 09:32

Venu Yanamandra

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0 and 1 are also integer constants. – Jim Balter Mar 09 '11 at 09:37
Thanks for pointing it right Jim. I seem to have read about some implications of enum w.r.t. typecast and directly conveyed it without looking at the real question. The one other demarkation would be the use of enums in block scope. – Venu Yanamandra Mar 11 '11 at 10:58
In C++, enums are separate types, but not in C. – Jim Balter Mar 11 '11 at 22:37

Why use enum when #define is just as efficient?

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