如何在C ++方法中定义const字符串

Question

Inside class, I would like to define some const strings.however the compiler reports error when I use

class A {
static const std::string s = "test" 
};

inside the class. How to do that? Do I have to define the const outside the class defination?

Answer 1

I think you have to define it outside.

class A {
  static const std::string s;
};

const std::string A::s("test");

Answer 2

Yes, it should be defined out side the class definition.

const std::string A::s = "test" ;

In C++0x initialization is allowed in the class definition itself ( result 1 ) . But I don't why for std::string type it isn't allowed ( result 2 ).

Ahh .. from the error message it seems it is allowed only for integral data types.

Answer 3

You initialize the static member outside the class (unlike C# where you can declare and initialize a member at the same place).

class A {
static const std::string s;
};

// initialize your static members outside of the class definition.
const std::string A::s = "Some text here";