类中的静态字符串常量与常量的命名空间 [c++]

I want to declare string constants that will be used across various classes in the project. I am considering two alternatives

Option 1:

#header file 
class constants{
    static const string const1;
};

#cpp file

const string constants::const1="blah";

Option 2:

#header file 
namespace constants{
    static const string const1="blah";
};

Just wondering what would be a better implementation.

Already looked at

Where to store Class Specific named constants in C++

Where to put constant strings in C++: static class members or anonymous namespaces

---

UPDATE:

Option 3:

Based on the suggestions from "potatoswatter" and "sellibitze" i currently have the following implementation?

#header file
namespace constants{
    extern const string& const1(); //WORKS WITHOUT THE EXTERN  ***WHY***
};

#cpp file
namespace constants{
   const string& const1(){static string* str = new string ("blah"); return *str;}
}

I'm including the header file where i need to use the constants. Are there any major cons of this implementation?

解决方案

^{Update 2 years later:}

Every global accessible by more than one source file should be wrapped in an inline function so the linker shares the object between the files, and the program initializes it properly.

inline std::string const &const1() {
    static std::string ret = "hello, world!";
    return ret;
}

The inline function is implicitly extern and may be wrapped in a named namespace or a class, if you like. (But don't use a class just to hold static members, as namespaces are better for that. And don't use an anonymous namespace as that would defeat the linker, and each source would see a different std::string object.)