Static member in the header-only library

Question

I am creating a library for the header only and I have to use a static member.
Is it possible to define it in the header file without overriding warning?

Answer 1

Assuming you are talking about a static data member, since a static member of a function is not a problem, there are various methods for different cases:

• Simple integral type const,, address not accepted:
  Give it a value in the declaration in the class definition. Or you can use a type enum.

• Another type, logically persistent:
  Use C ++ 11 constexpr.

• , constexpr:
  Meyers.

:

class Foo
{
private:
    static
    auto n_instances()
        -> int&
    {
         static int the_value;
         return the_value;
    }
public:
    ~Foo() { --n_instances(); }
    Foo() { ++n_instances(); }
    Foo( Foo const& ) { ++n_instances(); }
};

:

template< class Dummy >
struct Foo_statics
{
    static int n_instances;
};

template< class Dummy >
int Foo_statics<Dummy>::n_instances;

class Foo
    : private Foo_statics<void>
{
public:
    ~Foo() { --n_instances; }
    Foo() { ++n_instances; }
    Foo( Foo const& ) { ++n_instances; }
};

: .