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Establishes a socket connection by trying each endpoint in a sequence.
template< typename Protocol, typename Executor, typename Iterator, typename ConnectCondition> Iterator connect( basic_socket< Protocol, Executor > & s, Iterator begin, Iterator end, ConnectCondition connect_condition);
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.
An iterator pointing to the start of a sequence of endpoints.
An iterator pointing to the end of 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 boost::system::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.
An iterator denoting the successfully connected endpoint.
Thrown on failure. If the sequence is empty, the associated error_code
is boost::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 boost::system::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 boost::asio::connect
function as follows:
tcp::resolver r(my_context); tcp::resolver::query q("host", "service"); tcp::resolver::results_type e = r.resolve(q); tcp::socket s(my_context); tcp::resolver::results_type::iterator i = boost::asio::connect( s, e.begin(), e.end(), my_connect_condition()); std::cout << "Connected to: " << i->endpoint() << std::endl;