Sharing enums in c++ over classes

Question

I have a few enums in my program and I want to share it across different classes.

When I tried to define it in each class I got a "redefining" error.

Then I searched Google and saw that I should put it in a different header. I tried to to do that and included the header into every class header - I still got the same error.

Searched some more and found in StackOverflow a thread saying I should put them in their own namespace. So I tried:

enum.h:

namespace my_enums
{
enum classification {DATA_STORAGE,DMS,E_COMMERCE,GAMING,RTES,SECURITY};
enum skill { CPP, JAVA, SCRIPT, WEB, SYSTEM, QA };
enum company_policy {CHEAP, LAVISH, COST_EFFECTIVE};
}

But that still doesn't work: First, if tell classes that include the header to: "using namespace my_enums;" I get " is ambiguous" error.

What is the correct way to do what I'm trying to do?

Thanks in advance ^_^

Did you remember the multiple inclusion guard (#ifndef FOO,#define FOO,(...code...),#endif)? — thiton, Nov 14 '11 at 08:47
Do you protect the _enum.h_ file with [include guards](http://en.wikipedia.org/wiki/Include_guard)? — Some programmer dude, Nov 14 '11 at 08:47
@ thiton, @ Joachim Pileborg - sorry guys, I'm too much of a scrub and I have no idea what are inclusion guards, I'll try google it and will appreciate a simple explanation. — Lost_DM, Nov 14 '11 at 08:49
Thanks guys!! A quick Wiki search has explained everything. @thiton - since you replied first, if you can post an answer I will be glad to accept it ^_^ — Lost_DM, Nov 14 '11 at 08:51

score 7 · Accepted Answer · answered Nov 14 '11 at 08:52

7

Did you remember the multiple inclusion guard? Normally looks like:

#ifndef MY_HEADER_FILE_H
#define MY_HEADER_FILE_H
[...code...]
#endif

and protects types and enums from getting defined multiply in a compilation unit.

answered Nov 14 '11 at 08:52

thiton

35,651
4
70
100

score 5 · Answer 2 · edited Nov 14 '11 at 08:52

You only need to declare your enums once in a header if you wish and include that header where you use the enums:

//enum.h:
//include guards:
#ifndef MY_ENUMS
#define MY_ENUMS
namespace my_enums
{
enum classification {DATA_STORAGE,DMS,E_COMMERCE,GAMING,RTES,SECURITY};
enum skill { CPP, JAVA, SCRIPT, WEB, SYSTEM, QA };
enum company_policy {CHEAP, LAVISH, COST_EFFECTIVE};
}
#endif

//A.h

#include "enum.h"
class A
{
   void check()
   {
      my_enums::skill val = my_enums::SCRIPT;
   } 
};

score 1 · Answer 3 · answered Nov 14 '11 at 08:50

1

Maybe you've included it more then once?

Don't forget to add "guards" on include

#ifndef MY_ENUM_H_
#define MY_ENUM_H_

.... enter your enums here ...
#endif // MY_ENUM_H_

answered Nov 14 '11 at 08:50

Sergei Nikulov

5,029
23
36

score 0 · Answer 4 · edited Mar 24 '15 at 11:41

struct Classification
{
    enum Enum{ dataStorage, dms, eCommerce, gaming, rtes, security }
};

struct Skill
{
    enum Enum{ cpp, java, script, web, system, qa };
};

struct CompanyPolicy
{
    enum Enum{ cheap, lavish, cost_effective };
};

void whatever( Classification::Enum classification ) {}

class A
    : protected Classification
{
public:
    void foo() { whatever( dataStorage ); }
};

class B
{
public:
    void foo() { whatever( Classification::dataStorage ); }
};

Sharing enums in c++ over classes

4 Answers4

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