### 7.3 Using the C++ standard library ¶

An implementation of the C++ standard library is provided as a part of GCC. The following program uses the standard library `string` class to reimplement the Hello World program:

    #include <string>
    #include <iostream>

    using namespace std;

    int
    main ()
    {
      string s1 = "Hello,";
      string s2 = "World!";
      cout << s1 + " " + s2 << '\n';
      return 0;
    }

The program can be compiled and run using the same commands as above:

    $ g++ -Wall hellostr.cc
    $ ./a.out
    Hello, World!

Note that in accordance with the C++ standard, the header files for the C++ library itself do not use a file extension. The classes in the library are also defined in the `std` namespace, so the directive `using namespace std` is needed to access them, unless the prefix `std::` is used throughout (as in the previous section).