namespace

1#include <iostream>
2
3using namespace std;
4
5namespace {
6int x;
7void display();
8}
9
10namespace{
11void display(){
12cout << "x is "<<x<<endl;
13}
14}
15
16int main()
17{
18    x = 25;
19    display();
20    return 0;
21}
22
23 

1// namespaces
2#include <iostream>
3using namespace std;
4
5namespace foo
6{
7  int value() { return 5; }
8}
9
10namespace bar
11{
12  const double pi = 3.1416;
13  double value() { return 2*pi; }
14}
15
16int main () {
17  cout << foo::value() << '\n';
18  cout << bar::value() << '\n';
19  cout << bar::pi << '\n';
20  return 0;
21}

1namespace Parent
2{
3    inline namespace new_ns
4    {
5         template <typename T>
6         struct C
7         {
8             T member;
9         };
10    }
11     template<>
12     class C<int> {};
13}
14

1//Header.h
2#include <string>
3
4namespace Test
5{
6    namespace old_ns
7    {
8        std::string Func() { return std::string("Hello from old"); }
9    }
10
11    inline namespace new_ns
12    {
13        std::string Func() { return std::string("Hello from new"); }
14    }
15}
16
17#include "header.h"
18#include <string>
19#include <iostream>
20
21int main()
22{
23    using namespace Test;
24    using namespace std;
25
26    string s = Func();
27    std::cout << s << std::endl; // "Hello from new"
28    return 0;
29}
30