using例子

#include<iostream>

using namespace std;

namespace game1
{
int id = 10;
};

namespace game2
{
int id = 20;
};

void testHowUse()
{
  cout << game1::id << endl;
  cout << game2::id << endl;
}

void selectWho1(){
  using namespace game1;
  cout << id << endl;

  using namespace game2;
  //cout << id <<endl;//compiler error:id is ambiguous

  //use using avoid ambiguous
  using game2::id;
  cout << id<<endl;
  //or
  cout << game2::id<<endl;//add namespace game2 avoid ambiguous
}

void selectWho2(){
  using namespace game1;
  using namespace game2;
  //cout<<id<<endl; //error  id is ambiguous

  //add namespace avoid ambiguous
  cout << game1::id << endl;
  cout << game2::id << endl;

  //or
  using game1::id;
  cout << id << endl;
  //
  //using game2::id; //error  already using id  conflight
  cout << id << endl;
}
int main()
{
  //testHowUse();
  selectWho1();
  return 0;
}