Restricting `using` directives to the current file

问题

Sorry for this silly question, but is there any way to restrict using directives to the current file so that they don't propagate to the files that #include this file?

回答1:

Perhaps wrapping the code to be included inside its own namespace could achieve the behavior
you want, since name spaces have scope affect.

// FILENAME is the file to be included
namespace FILENAME_NS {
   using namespace std;
   namespace INNER_NS {
      [wrapped code]
   }
}
using namespace FILENAME_NS::INNER_NS;

and in some other file

#include <FILENAME>
// std namespace is not visible, only INNER_NS definitions and declarations
...

回答2:

No, there isn't, which is why you should not use using directives in header files, or any other file that you #include.

回答3:

Technically you should be able to import them to some internal namespace, and then make the things declared in that visible in the namespace meant for the user.

#ifndef HEADER_HPP
#define HEADER_HPP

#include <string>

namespace my_detail
{
    using std::string;
    inline string concatenate(const string& a, const string& b) { return a + b; }   
}

namespace my_namespace
{
    using my_detail::concatenate;
}

#endif

---

#include <iostream>
#include "header.hpp"

using namespace my_namespace;

int main() 
{
    std::  //required
    string a("Hello "), b("world!");
    std::cout << concatenate(a, b) << '\n';
}

Not sure if it is worth the trouble and how well it plays with "argument-dependent lookup".

来源：https://stackoverflow.com/questions/2577557/restricting-using-directives-to-the-current-file