define static string variable in c++ class

Question

I have 2 questions:

Why is this possible for an int variable:

foo.h:

class foo{

     private:
        const static int a = 42;
};

but for a string variable I need to do it this way?

foo.h:

class foo{

     private:
        static string fooString;
};

foo.cpp:

string foo::fooString = "foo";

---

And also:

In my particular case foo::fooString should represent a path variable, and I would like that for every object of class foo there were just one instance of foo::string, representing a const value that should never change.

Is there another way to solve this problem?

Answer 1

Why is this possible for an int variable: [..] but for a string variable I need to do it this way?

Just because. Actually you can still make the string const but, yes, you have to define it outside of the class definition. You can only do in-place initialisation of static members when they are const and integral (or "of literal type").

(In C++11 you can even do it for non-static non-const members when they are of literal type.)

I would like that for every object of class foo there were just one instance of foo::string, representing a const value that should never change. Is there another way to solve this problem?

A static const std::string, as you might expect.

// C++03
struct T {
   static const std::string foo;
};

const std::string T::foo = "lol";