##### ip::basic_resolver::async_resolve (3 of 5 overloads)

Asynchronously perform forward resolution of a query to a list of entries.

    template<
        typename ResolveToken = default_completion_token_t<executor_type>>
    DEDUCED async_resolve(
        const protocol_type & protocol,
        string_view host,
        string_view service,
        ResolveToken && token = default_completion_token_t< executor_type >());

This function is used to resolve host and service names into a list of endpoint entries. It is an initiating function for an asynchronous operation, and always returns immediately.

###### Parameters

protocol

  A protocol object, normally representing either the IPv4 or IPv6 version of an internet protocol.

host

  A string identifying a location. May be a descriptive name or a numeric address string. If an empty string and the passive flag has been specified, the resolved endpoints are suitable for local service binding. If an empty string and passive is not specified, the resolved endpoints will use the loopback address.

service

  A string identifying the requested service. This may be a descriptive name or a numeric string corresponding to a port number. May be an empty string, in which case all resolved endpoints will have a port number of 0.

token

  The completion token that will be used to produce a completion handler, which will be called when the resolve completes. Potential completion tokens include `use_future`, `use_awaitable`, `yield_context`, or a function object with the correct completion signature. The function signature of the completion handler must be:

      void handler(
        const asio::error_code& error, // Result of operation.
        resolver::results_type results // Resolved endpoints as a range.
      );

  Regardless of whether the asynchronous operation completes immediately or not, the completion handler will not be invoked from within this function. On immediate completion, invocation of the handler will be performed in a manner equivalent to using `async_immediate`.

A successful resolve operation is guaranteed to pass a non-empty range to the handler.

###### Completion Signature

    void(asio::error_code, results_type)

###### Remarks

On POSIX systems, host names may be locally defined in the file `/etc/hosts`. On Windows, host names may be defined in the file `c:\windows\system32\drivers\etc\hosts`. Remote host name resolution is performed using DNS. Operating systems may use additional locations when resolving host names (such as NETBIOS names on Windows).

On POSIX systems, service names are typically defined in the file `/etc/services`. On Windows, service names may be found in the file `c:\windows\system32\drivers\etc\services`. Operating systems may use additional locations when resolving service names.