async_connect (3 of 6 overloads)

Asynchronously establishes a socket connection by trying each endpoint in a sequence.

template<
    typename Protocol,
    typename Iterator,
    typename IteratorConnectHandler>
DEDUCED async_connect(
    basic_socket< Protocol > & s,
    Iterator begin,
    Iterator end,
    IteratorConnectHandler && handler);

This function attempts to connect a socket to one of a sequence of endpoints. It does this by repeated calls to the socket's async_connect member function, once for each endpoint in the sequence, until a connection is successfully established.

Parameters

s

The socket to be connected. If the socket is already open, it will be closed.

begin

An iterator pointing to the start of a sequence of endpoints.

end

An iterator pointing to the end of a sequence of endpoints.

handler

The handler to be called when the connect operation completes. Copies will be made of the handler as required. The function signature of the handler must be:

void handler(
  // Result of operation. if the sequence is empty, set to
  // boost::asio::error::not_found. Otherwise, contains the
  // error from the last connection attempt.
  const boost::system::error_code& error,

  // On success, an iterator denoting the successfully
  // connected endpoint. Otherwise, the end iterator.
  Iterator iterator
);

Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using boost::asio::io_context::post().

Example

std::vector<tcp::endpoint> endpoints = ...;
tcp::socket s(io_context);
boost::asio::async_connect(s,
    endpoints.begin(), endpoints.end(),
    connect_handler);

// ...

void connect_handler(
    const boost::system::error_code& ec,
    std::vector<tcp::endpoint>::iterator i)
{
  // ...
}