How to get the number of elements of an enum?

Question

4.00/5 (1 vote)

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Hello,
I have created one struture like,

typedef enum
{
   NAME = 0,
   ADDRESS,
   BIRTHDATE,
}INFORMATION

And I want to get Number of elements in this structure. Is there any function?

Posted 7-Jun-11 19:14pm

Ruchira Patel

Updated 26-Feb-19 23:49pm

CPallini

v3

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5 solutions

Solution 2

Considering the structure that is given by you is:

typedef enum
{
MIN = 0,
NAME  = MIN,
ADDRESS,
BIRTHDATE,
MAX = BIRTHDATE
};
int NumOfElement = MAX-MIN+1;

Or directly BIRTHDATE + 1 (if Enum start with 0).

Posted 7-Jun-11 20:27pm

ShilpiP

Updated 7-Jun-11 20:30pm

v2

Comments

Sergey Alexandrovich Kryukov 8-Jun-11 3:12am

This is improved variant of what I suggested, my 5.
All problems we're discussing here is C/C++ legacy of enum type which is not "real" enumeration type. All the details in my article "Enumeration Types do not Enumerate!":
http://www.codeproject.com/KB/dotnet/EnumTypesDoNotEnumerate.aspx

--SA

ShilpiP 8-Jun-11 3:22am

Thanks for 5. I was unaware of your discussion. Let me check.

CPallini 8-Jun-11 5:53am

I would prefer NAME=0, MIN=NAME.

Solution 3

In the way you asked ... NO.
There is no function (code to be executed) that can give such a result, since standard C++ has no reflection.
The standard RTTI is tailored to support dynamic_cast and have no role on enums.

Things may be different if we consider some language extensions (like C++/CLI, that is an ECMA standard not accepted by ANSI that is the owner of the C++ standard ...) that can add reflection and hence the capability to query at runtime the state of the source.

Of course there can be tricks like

enum E
{
    a,b,c, count;
};

That leads to a=0, b=1, c=2, count=3. But that's a different thing respect to what you asked (may be not adequate, for certain purpose).

Posted 7-Jun-11 21:17pm

Emilio Garavaglia

Updated 8-Jun-11 3:55am

v2

Solution 4

I am agree with SA, however while doing generic programming and thinking about future extensibility, we always add eENUMLast in enum, so that if we add/delete any enumerated value, eENUMLast always remain last.

Posted 7-Jun-11 23:35pm

ThatsAlok

Solution 5

Enum.GetNames(typeof(INFORMATION)).Count()

It will be helpful. Even though you will increase decrease values in enum It will give correct result.

Posted 26-Feb-19 23:49pm

Ankesh Gamit

Comments

Maciej Los 27-Feb-19 6:33am

My vote of 1. This is not a C++ code!
A C++ version is bit different. See: Enum.GetNames(Type) Method (System) | Microsoft Docs[^]

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Sergey Alexandrovich Kryukov · Accepted Answer · 2011-06-07T19:24:00

Solution 1

You rather need a simple technique commonly used in such cases.

C++

enum Information {
   NAME = 0,
   ADDRESS,
   BIRTHDATE,
   Length,
};

//...

for (int index = NAME; index < Length; ++index) {
   // use index as 
}

—SA

Posted 7-Jun-11 19:24pm

Sergey Alexandrovich Kryukov

Updated 8-Jun-11 6:56am

v2

Comments

Resmi Anna 8-Jun-11 1:36am

Why should we go for this?
int NumberOfElm = Length - NAME;
is enough rt?
what if the enum looks like
enum Information {
NAME = 0,
ADDRESS,
BIRTHDATE = 100,
Length,
};
also i feel this question doesnt make any sense like number of elements in array or list. because i havent heard of anything like dynamic enum in c++. is there anything like that??

Niklas L 8-Jun-11 2:30am

IMO it's rather clear that the OP doesn't have BIRTHDATE = 100. The dynamic enums are not dynamic during runtime, but rather during the evolution of the software. I can think of several situations where this comes in handy. Not being able to tell the number of items in an enumerable sequence is a severe limitation.

Resmi Anna 8-Jun-11 2:42am

what role the number of elements in enum plays?Its value is important rt?
sorry if i am wrong.
any real situation that needs the number of elemnts in enum?

Niklas L 8-Jun-11 3:08am

You can use the enum values to index arrays, in which case knowing the bounds is crucial. Implementation of a deck of cards is a classical example. It is not likely however, that someone will introduce a new suit with a new version of the software, but imagine the same thing where the enum is representing a state which can be expanded in future versions. Not being able to programatically tell the number of items in the sequence is a great source for errors.

Resmi Anna 8-Jun-11 4:56am

Not here for a dispute:):)..just to share our views.

Deck of card is classical example on the usage of enum.

I am asking is there any point at which we need to know the number of elements in an enum dynamically?

like suppose we have a character array in our programchar str[50];

At execution point 1 it may contain the string"Hi"

At execution point 2 it may contain the string"Hello"

so we should have some function to know the length of an array.

correct till here??

suppose your array conatins the value "Hi" throught the program execution.If are quite sure about that, you can use

const int Lenth = 2;

No need to write a GetLenght() function.It will only add a performance hit.

agreeing??suppose your Hi becomes "Hello" in your software version 2.

then you can modify const int Lenth = 5.

here also we consider performance than avoiding one line codeagreeing??

so like this is there any chance that at execution point1 your enum contains 4 elemnts and at execution point 2 enum conatins 5 elemnts?Then only you need to bother about calculating

the number of items of an enum rt?someone understood:(:(?????

Niklas L 8-Jun-11 5:54am

I do understand your point, and technically you're right. I'm saying that the lack language support of this information is a source of errors. If you add a new value to your enumeration sequence, you will also have to update another value somewhere else, the const int Length in your case. You might introduce very hard to catch bugs if you forget this. It's a maintenance issue. This is where constructs like this comes in handy. It's far from a perfect solution, for reasons given, but it works quite well and is common practice in C/C++.

Sergey Alexandrovich Kryukov 8-Jun-11 12:59pm

I totally agree. This is a typical C++ cheating about enum. In languages with real enumeration (Ada, Pascal) you have all that. With C++, a simple technique SP 24 or I show is the best, practically. It imposes limitations and needs discipline, but what else can be done?
--SA

Sergey Alexandrovich Kryukov 8-Jun-11 3:11am

Of course you're right. All problems we're discussing here is C/C++ legacy of enum type which is not "real" enumeration type.
All the details in my article "Enumeration Types do not Enumerate!":
http://www.codeproject.com/KB/dotnet/EnumTypesDoNotEnumerate.aspx
--SA

Sergey Alexandrovich Kryukov 8-Jun-11 3:14am

True, but Anna is right in general. All variants of such techniques suffer from limitation. Please see my comment below and my article on the topic. It's C#, but C legacy is discussed.
--SA

Albert Holguin 8-Jun-11 10:35am

this is meant to support better software evolution, as Niklas suggested, for example, if in the future, you add two enumerated values, any loops or case statements that use MIN and MAX wouldn't have to change, they'd already be functional after the addition of new elements

Sergey Alexandrovich Kryukov 8-Jun-11 18:26pm

Good note. Yes, this is the main point about it.
--SA

Legor 8-Jun-11 3:06am

I agree on that solution. You'll need some length, or MAX as last component of your enum to determine the number of elements. Given that the numerations are simple 1-increments.

Sergey Alexandrovich Kryukov 8-Jun-11 3:15am

Thank you very much.
Please see my comments above and my article.
--SA