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Understanding how to correctly treat c++ class constants

Asked 2011-04-11T10:53:03.187
24

Consider the following:

namespace MyNamespace{
class MyClass {
public:
   // Public area
private:
   // Private area
protected:
   // Protected area
}; /* Class */
} /* Namespace */

And consider that I would like to define a constant which is specific for my class. I usually do the following:

namespace MyNamespace{
// Constants
const int MYINT = 12;
const std::string MYSTR = std::string("Hello");
// Class definition
class MyClass {
public:
   // Public area
private:
   // Private area
protected:
   // Protected area
}; /* Class */
} /* Namespace */

In this way I can get my variable in this way (somewhere in my code):

MyNamespace::MYINT;
MyNamespace::MYSTR;

Is this a good practice?
Considering that constants can be treated in several ways (for example numeric constants are often treated using enum), what is the best approach to define a constant (related to a class, but that can be also useful somewhere else) ?

c++ class constants
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1 Answer

5

There is no "best" solution as of course that is a very subjective term.

Considering that you mention the constants being used somewhere else, we can say that they should be declared in either the protected (if they are to be used exclusively by derived classes) or more likely the public section of the class.

Constants that are not of integer type should be defined as static const members (but you will have to be careful of the order of static initialization if there are any other static objects that refer to these constants).

Constants of integer type can either be declared as static const int or as enums, as you already mention. The discriminating factor here is whether two or more constants can be logically grouped together.

For example, this is probably a good idea:

class MyClass {
    public:
        enum {
            Color_Red,
            Color_Green,
            Color_Blue,
        };
};

While this is not:

class MyClass {
    public:
        enum {
            Color_Red,
            Vehicle_Car,
        };
};
answered 2011-04-11T11:06:46.767

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