| [/ |
| / Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com) |
| / |
| / Distributed under the Boost Software License, Version 1.0. (See accompanying |
| / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
| /] |
| |
| [section:ResolveHandler Resolve handler requirements] |
| |
| A resolve handler must meet the requirements for a [link asio.reference.Handler |
| handler]. A value `h` of a resolve handler class should work correctly in the |
| expression `h(ec, r)`, where `ec` is an lvalue of type `const error_code` and |
| `r` is an lvalue of type `const ip::basic_resolver_results<InternetProtocol>`. |
| `InternetProtocol` is the template parameter of the [link |
| asio.reference.ip__basic_resolver `ip::basic_resolver<>`] which is used to |
| initiate the asynchronous operation. |
| |
| [heading Examples] |
| |
| A free function as a resolve handler: |
| |
| void resolve_handler( |
| const asio::error_code& ec, |
| asio::ip::tcp::resolver::results_type results) |
| { |
| ... |
| } |
| |
| A resolve handler function object: |
| |
| struct resolve_handler |
| { |
| ... |
| void operator()( |
| const asio::error_code& ec, |
| asio::ip::tcp::resolver::results_type results) |
| { |
| ... |
| } |
| ... |
| }; |
| |
| A lambda as a resolve handler: |
| |
| resolver.async_resolve(..., |
| [](const asio::error_code& ec, |
| asio::ip::tcp::resolver::results_type results) |
| { |
| ... |
| }); |
| |
| A non-static class member function adapted to a resolve handler using |
| `std::bind()`: |
| |
| void my_class::resolve_handler( |
| const asio::error_code& ec, |
| asio::ip::tcp::resolver::results_type results) |
| { |
| ... |
| } |
| ... |
| resolver.async_resolve(..., |
| std::bind(&my_class::resolve_handler, |
| this, std::placeholders::_1, |
| std::placeholders::_2)); |
| |
| A non-static class member function adapted to a resolve handler using |
| `boost::bind()`: |
| |
| void my_class::resolve_handler( |
| const asio::error_code& ec, |
| asio::ip::tcp::resolver::results_type results) |
| { |
| ... |
| } |
| ... |
| resolver.async_resolve(..., |
| boost::bind(&my_class::resolve_handler, |
| this, asio::placeholders::error, |
| asio::placeholders::results)); |
| |
| [endsect] |