Re: typedefed enum

PSN wrote:


First in C++, using the typedef here is unnecessary. Just do this to
acheive the same effect:

 enum test
 {
   // ...
 };

However, you can't add new elements to an existing enum. You'll either
have to modify the existing definition, or, if that is not allowed,
create a new enum. You can use the same names if you put it in a
different scope. For instance:

 typedef enum test1
 {
  hcone = 0,
  hctwo
  hcthree
 } test;

 namespace MyTest
 {
   enum test
   {
     hcone = ::hcone,
     hctwo = ::hctwo
     hcthree = ::hcthree,
     hcsize
   };
 }

Which you can use fully qualified:

 void Foo( MyTest::test );

Instead of adding the size to the end, however, I generally prefer to
have a separate enum because the size is technically an invalid value
in the enum that could be used like this:

  Foo( MyTest::hcsize );

Because of this, every user of your enum (e.g. Foo) needs to check the
value of the enum to make sure it is within range (i.e., != hcsize). If
instead you do this:

 enum MyEnum
 {
   MY_MIN,
   MY_ONE = MY_MIN,
   MY_TWO,
   MY_THREE,
   MY_MAX = MY_THREE
 };
 enum { MY_SIZE = (MY_MAX - MY_MIN) + 1 };

Then you avoid the problem mentioned above, but you know the size and
can easily iterate on the enum values (assuming the enum values go in
order, of course):

 std::vector<MyEnum> v( MY_SIZE, MY_ONE );
 // ...

 for( int m=MY_MIN; m <= MY_MAX; ++m )
 {
   // ...
 }

 // Or if you need m to be of the enum type...
 for( MyEnum m=MY_MIN; m <= MY_MAX; m = MyEnum( m + 1 ) )
 {
   // ...
 }

Unfortunately, with this technique, you have to remember to update the
min and max values if you change the enum, but that is still easier
IMHO than relying on the user to check the validity of the enum value,
which is all too easy to omit.

Cheers! --M