unnamed enum & typedef?

Question

I was getting a little confused with typedef/enum until I realised that I did not need to name the emun. Are there any differences / benefits between these two when used with typedef, the 2nd one to me seems a lot easier to understand.

First Example:

typedef enum enumMenuItems {
    none,
    add,
    save,
    load,
    list,
    remove
} menuItems;

menuItems optionSelect = none;

Second Example:

typedef enum {
    Earth = 1, 
    Mars,
    Saturn,
    Neptune,
    Jupiter
} planets;

planets closest = Mars;

.

EDIT:

typedef enum enumMenuItems {
    none,
    add,
    save,
    load,
    list,
    remove
} menuItems;

So the above essentially defines two types, one an enum called enumMenuItems and the second a typedef of enumMenuItems called menuItems.

menuItems optionSelect = save;
enum enumMenuItems optionSelect = save;

The above two declarations are essentially the same, one using the typedef and the other using the enum. So if your using a typedef you can leave your enum unnamed as the type can be accessed via the typedef menuItem.

gary

Answer 1

The first case allows you to refer to the type as enum enumMenuItems. For example:

enum enumMenuTimes optionSelect = none;

It might be clearer if you break it down into two parts:

enum _planets { 
    Earth = 1, 
    Mars, 
    Saturn,
    Neptune,
    Jupiter
};
typedef enum _planets planets;

enum _planets planet1 = Earth;
planets       planet2 = Mars;

If that simplifies the concept for you. Your second notation there is just shorthand; it creates an anonymous enumeration and then uses typedef to give it a name. You could even, for example, do:

enum {
    Value0,
    Value1,
    Value2
};

But you'd not be able to use the enumeration as a fake type name, like you're trying to do. You can still access the enumerated values, though.

A more in depth description is available at the comp.lang.c FAQ.