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.


hostNameOrAddress is nullptr.


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.

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 HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

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 );
 //     }

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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