BeginGetHostEntry Method (String, AsyncCallback, Object)

Dns::BeginGetHostEntry Method (String^, AsyncCallback^, Object^)


Asynchronously resolves a host name or IP address to an IPHostEntry instance.

Namespace:   System.Net
Assembly:  System (in System.dll)

[HostProtectionAttribute(SecurityAction::LinkDemand, ExternalThreading = true)]
static IAsyncResult^ BeginGetHostEntry(
	String^ hostNameOrAddress,
	AsyncCallback^ requestCallback,
	Object^ stateObject


Type: System::String^

The host name or IP address to resolve.

Type: System::AsyncCallback^

An AsyncCallback delegate that references the method to invoke when the operation is complete.

Type: System::Object^

A user-defined object that contains information about the operation. This object is passed to the requestCallback delegate when the operation is complete.

Return Value

Type: System::IAsyncResult^

An IAsyncResult instance that references the asynchronous request.

Exception Condition

hostNameOrAddress is null.


The length of hostNameOrAddress is greater than 255 characters.


An error is encountered when resolving hostNameOrAddress.


hostNameOrAddress is an invalid IP address.

The BeginGetHostEntry method queries a DNS server for the IP address that is associated with a host name or IP address.

Note   This member emits trace information when you enable network tracing in your application. For more information, see Network Tracing in the .NET Framework.

The asynchronous BeginGetHostEntry operation must be completed by calling the EndGetHostEntry method. Typically, the method is invoked by the requestCallback delegate.

This method does not block until the operation is complete. To block until the operation is complete, use the GetHostEntry method.

For detailed information about using the asynchronous programming model, see Calling Synchronous Methods Asynchronously.

The following code example uses the BeginGetHostEntry method to resolve an IP address to an IPHostEntry instance.

   // Signals when the resolve has finished.
   static ManualResetEvent^ GetHostEntryFinished =
      gcnew ManualResetEvent( false );

   // define the state object for the callback. 
   // use hostName to correlate calls with the proper result.
   ref class ResolveState
      String^ hostName;
      IPHostEntry^ resolvedIPs;

      ResolveState( String^ host )
         hostName = host;

      property IPHostEntry^ IPs 
         IPHostEntry^ get()
            return resolvedIPs;
         void set( IPHostEntry^ IPs )
            resolvedIPs = IPs;

      property String^ host 
         String^ get()
            return hostName;
         void set( String^ host )
            hostName = host;

   // Record the IPs in the state object for later use.
   static void GetHostEntryCallback( IAsyncResult^ ar )
      ResolveState^ ioContext = (ResolveState^)( ar->AsyncState );

      ioContext->IPs = Dns::EndGetHostEntry( ar );

   // Determine the Internet Protocol(IP) addresses for this 
   // host asynchronously.
   static void DoGetHostEntryAsync( String^ hostName )
      ResolveState^ ioContext = gcnew ResolveState( hostName );

      Dns::BeginGetHostEntry( ioContext->host,
         gcnew AsyncCallback( GetHostEntryCallback ), ioContext );
      // Wait here until the resolve completes 
      // (the callback calls .Set())

      Console::WriteLine("EndGetHostEntry({0}) returns:", ioContext->host);

      for (int i = 0; i < ioContext->IPs->AddressList->Length; i++)
		Console::WriteLine("    {0}", ioContext->IPs->AddressList[i]->ToString());			

//      for each ( IPAddress^ ip in ioContext->IPs )
 //     {
 //        Console::WriteLine( "{0} ", ip );
 //     }

for accessing DNS information. Associated enumeration: PermissionState::Unrestricted

.NET Framework
Available since 2.0
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