why does define conflict with enum class?

Question

Here is a small code in which the conflict occurs. is there any way to get around this correctly?

#define DEBUG 0

enum class TypeEnum : int
{
    DEBUG = 0,
    INFO = 1
};

There is also a standard(?) NDEBUG that you can use when compiling (meaning, if defined, it's a release build, otherwise it's a debug build). It's checked by standard functions like assert and you can use it in your own code too instead of #define DEBUG 0. — Ted Lyngmo
– Ted Lyngmo, Commented Aug 31, 2021 at 20:49

Remy Lebeau · Accepted Answer · 2021-08-31 21:18:13Z

6

It's the nature of the preprocessor. Lines beginning with # are commands to the preprocessor. #define is a command that defines a text replacement, which will rewrite your code when preprocessed. In this case, all instances of DEBUG will be replaced with 0, so the code becomes:

enum class TypeEnum : int
{
    0 = 0,
    INFO = 1
};

Which, of course, doesn't make sense.

edited Aug 31, 2021 at 21:18

Remy Lebeau

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answered Aug 31, 2021 at 20:45

Joseph Larson

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6 Comments

Олег Привалов Over a year ago

thank you, I will then choose unique names for the enum class, because define DEBUG is not in my code.

bolov Over a year ago

@ОлегПривалов by convention identifiers with ALL_CAPS are used for preprocessor macros, so just avoid declaring C++ identifiers with all caps.

Joseph Larson Over a year ago

@bolov That's only a convention, though. You can't depend on naming conventions, especially around enums.

bolov Over a year ago

@JosephLarsonI am not talking about a convention on enums. I am talking about a convention on macros. Because macros by convention are ALL_CAPS and name conflicts with macros are bad (as you saw) it's a best practice to not use ALL_CAPS for anything except macros. It's true sometimes this macros convention isn't followed (cough MSVC min, max cough cough) and that can wrecks havoc on code, but that is an exception. Even in those cases, it doesn't hurt to avoid ALL_CAPS for C++ names.

bolov Over a year ago

@JosephLarson If you are talking about inheriting a code base where enums are defined with ALL_CAPS, then yes, that's a problem and you need to take care of those enums when a conflict appears.

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