Why package a single enum in a struct?

Question

This is written by someone who has left the company. I can't see any reason to do this and am curious if there's something I am missing.

enum thing_type_e
{
   OPTION_A = 0,
   OPTION_B,
   OPTION_C,
   OPTION_D
};

struct thing_type_data_s
{
   enum_type_e mVariable;
};

I supposed it's possible he was going to add more to the structure, but after looking at how it is used, I don't think so.

Barring "he was going to add more to the structure," why package a single enum in a struct? Is there some motivation I'm not thinking of?

Update:

As asked in the comments, he used it in this fashion:

void process_thing_type(thing_type_data_s* ParamVariable)
{
    local_variable = ParamVariable->mVariable;
    ...
}

This was originally built with GCC 3.3.5 if it makes any difference.

I have seen this done before as well - I can't recall but I think it had something to do with simplifying debugging - you can see the possible values enumerated in the debugger maybe? — Mark Setchell
– Mark Setchell, Commented Jan 23, 2014 at 20:39
@WojtekSurowka Updated the question with an example... but it's really nothing special. I wonder if it is so he could see things better in GDB. — kmort
– kmort, Commented Jan 23, 2014 at 20:44
Possibly he just wasn't sure it was legal to pass a pointer to an enum. Enums definitely seem different from other types, I can see someone doing this to "play it safe". — AShelly
– AShelly, Commented Jan 23, 2014 at 20:51

juanchopanza · Accepted Answer · 2014-01-23 20:44:13Z

13

Possibly to enforce some type safety. Old-style enums are implicitly convertible to integral types, and this is not always desirable. Besides this, they are unscoped.

C++11 adds scoped enumerations (or "class" enums) to fix both of these issues.

Here's an example:

void foo(int) {}

int main()
{
  foo(OPTION_A);  // OK
  thing_type_data_s s = { OPTION_A };
  foo(s);  // Error
}

edited Jan 23, 2014 at 20:44

answered Jan 23, 2014 at 20:34

juanchopanza

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6 Comments

Timothy Shields Over a year ago

I think you missed that the enum declaration isn't nested in the struct. This isn't anything like what you're saying.

juanchopanza Over a year ago

@TimothyShields No, I didn't miss that. The main point is the implicit conversion to integral types. The scoping is another, unrelated, matter.

Marco A. Over a year ago

juancho wrote the same thing I thought of. Perhaps that guy thought "let's use the struct instead of the plain enum", without visibility scopes. Who knows..

kmort Over a year ago

I probably should have mentioned that he wrote it and built it with GCC 3.3.5.

juanchopanza Over a year ago

@KeithThompson an old-schoole enum values are in the enclosing scope. So enum Colour { Blue, Orange }; enum Fruit { Apple, Orange }; is an error. That is what I was referring to.

|

tommyo · Accepted Answer · 2014-01-23 20:41:37Z

0

Are there other structs with the same type of member first but different otherwise? He might be using the struct thing_type_data_s in a baseclass-y kind of way. But who knows, you tagged the question as both C and C++. I would make sense in C, at least.

answered Jan 23, 2014 at 20:41

tommyo

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1 Comment

kmort Over a year ago

No, there aren't. It was just this one struct. Thanks for the input.

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