Question

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Is there a reason to use enum to define a single constant in C++ code?

I just came across the following snippet in some old code, with an odd use of enum:-

class MyClass
{
public:
  enum {MAX_ITEMS=16};
  int things[MAX_ITEMS];
...
} ;

This is better than #define MAX_ITEMS 16 but is it any different from static const int MAX_ITEMS=16;?

Digging back into the mists of memory, I remember some C++ compilers not allowing you to initialize consts within the class, instead requiring a separate…

const int MyClass::MAX_ITEMS = 16;

… in the .cpp source file. Is this just an old workaround for that?

Answer 1

This is the age old “enum hack“ used to initialize arrays inside the class definition.

Traditionally, pre C++03 it was not possible to initialize a static const inside the class declaration. Since array declaration needs a compile time constant index in declaration. The enum hack was used as an workaround.

class A 
{
    enum { arrsize = 2 };
    static const int c[arrsize] = { 1, 2 };

};