What's the scope of the “using” declaration in C++?

Question

I\'m using the \'using\' declaration in C++ to add std::string and std::vector to the local namespace (to save typing unnecessary \'std::\'s).

using std::str         


        

Answer 1

The scope of the using statement depends on where it is located in the code:

• Placed at the top of a file, it has scope throughout that file.
• If this is a header file, it will have scope in all files that include that header. In general, this is "not a good idea" as it can have unexpected side effects
• Otherwise the using statement has scope within the block that contains it from the point it occurs to the end of the block. If it is placed within a method, it will have scope within that method. If it is placed within a class definition it will have scope within that class.