Establishes a socket connection by trying each endpoint in a sequence.
template< typename Protocol, typename Executor, typename EndpointSequence, typename ConnectCondition> Protocol::endpoint connect( basic_socket< Protocol, Executor > & s, const EndpointSequence & endpoints, ConnectCondition connect_condition, typename constraint< is_endpoint_sequence< EndpointSequence >::value >::type = 0);
This function attempts to connect a socket to one of a sequence of endpoints.
It does this by repeated calls to the socket's connect
member function, once for each endpoint in the sequence, until a connection
is successfully established.
The socket to be connected. If the socket is already open, it will be closed.
A sequence of endpoints.
A function object that is called prior to each connection attempt. The signature of the function object must be:
bool connect_condition( const asio::error_code& ec, const typename Protocol::endpoint& next);
The ec
parameter
contains the result from the most recent connect operation. Before
the first connection attempt, ec
is always set to indicate success. The next
parameter is the next endpoint to be tried. The function object should
return true if the next endpoint should be tried, and false if it
should be skipped.
The successfully connected endpoint.
Thrown on failure. If the sequence is empty, the associated error_code
is asio::error::not_found
.
Otherwise, contains the error from the last connection attempt.
The following connect condition function object can be used to output information about the individual connection attempts:
struct my_connect_condition { bool operator()( const asio::error_code& ec, const::tcp::endpoint& next) { if (ec) std::cout << "Error: " << ec.message() << std::endl; std::cout << "Trying: " << next << std::endl; return true; } };
It would be used with the asio::connect
function as follows:
tcp::resolver r(my_context); tcp::resolver::query q("host", "service"); tcp::socket s(my_context); tcp::endpoint e = asio::connect(s, r.resolve(q), my_connect_condition()); std::cout << "Connected to: " << e << std::endl;