How become the String in my sf::string
Please, inform yourself at least 20 seconds before you ask everything. Look at the documentation of sf::String, and there at the constructors. By the way, I already gave you the answer to this question in my last post.
Here is my code, but I think this is correct
Yes, it is. It might be that std::to_string() is not fully supported with the default options. Visual Studio 2010 doesn't support it either (actually it would, but they forgot the most important overloads :x), so using it compiler-independently is not possible yet anyway.