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A resolve handler must meet the requirements for a 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 ip::basic_resolver<>
which is used to initiate the asynchronous operation.
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));