Declaring Static Data Members of Type const std::string

In C , initializing a static data member of type const std::string directly within the class definition is not permitted. Instead, there are two options to define such data members:

Inline Variables (C 17 or Later)

Use an inline variable, which defines and initializes the static member within the class definition:

class A {
private:
  inline static const string RECTANGLE = "rectangle";
};

External Definition

Define the static member outside the class definition and provide the initializer in a separate implementation file:

Header File

class A {
private:
  static const string RECTANGLE;
};

Implementation File

const string A::RECTANGLE = "rectangle";

Limitations of In-Class Initialization

The syntax of initializing static data members within the class definition is only supported for integral and enum types. For non-integral types like const std::string, this approach is not valid.