I tried to compile HTTP Server from here <http://think-async.com/Asio/asio-1.11.0/doc/asio/examples/cpp11_examples.html#asio.examples.cpp11_examples.http_server> with gcc.
I used 

```
 g++ main.cpp -std=c++11 -I/home/gabi/Downloads/asio-1.11.0/include -pthread

```

I get this

```
/tmp/ccE1vIzF.o: In function `http::server::server::server(std::string const&, std::string const&, std::string const&)':
server.cpp:(.text+0x1a3): undefined reference to `http::server::connection_manager::connection_manager()'
server.cpp:(.text+0x1e0): undefined reference to `http::server::request_handler::request_handler(std::string const&)'
/tmp/ccE1vIzF.o: In function `http::server::server::do_accept()::{lambda(std::error_code)#1}::operator()(std::error_code) const':
server.cpp:(.text+0x52a): undefined reference to `http::server::connection_manager::start(std::shared_ptr<http::server::connection>)'
/tmp/ccE1vIzF.o: In function `http::server::server::do_await_stop()::{lambda(std::error_code, int)#1}::operator()(std::error_code, int) const':
server.cpp:(.text+0x5e9): undefined reference to `http::server::connection_manager::stop_all()'
/tmp/ccE1vIzF.o: In function `_ZN9__gnu_cxx13new_allocatorIN4http6server10connectionEE9constructIS3_IN4asio19basic_stream_socketINS6_2ip3tcpENS6_21stream_socket_serviceIS9_EEEERNS2_18connection_managerERNS2_15request_handlerEEEEvPT_DpOT0_':
server.cpp:(.text._ZN9__gnu_cxx13new_allocatorIN4http6server10connectionEE9constructIS3_IN4asio19basic_stream_socketINS6_2ip3tcpENS6_21stream_socket_serviceIS9_EEEERNS2_18connection_managerERNS2_15request_handlerEEEEvPT_DpOT0_[_ZN9__gnu_cxx13new_allocatorIN4http6server10connectionEE9constructIS3_IN4asio19basic_stream_socketINS6_2ip3tcpENS6_21stream_socket_serviceIS9_EEEERNS2_18connection_managerERNS2_15request_handlerEEEEvPT_DpOT0_]+0x8b): undefined reference to `http::server::connection::connection(asio::basic_stream_socket<asio::ip::tcp, asio::stream_socket_service<asio::ip::tcp> >, http::server::connection_manager&, http::server::request_handler&)'
collect2: error: ld returned 1 exit status

```

Does anyone know why?
if I try to compile <http://think-async.com/Asio/asio-1.11.0/doc/asio/examples/cpp11_examples.html#asio.examples.cpp11_examples.allocation> works.