This documentation is archived and is not being maintained.

Socket.EndSendTo Method

Ends a pending asynchronous send to a specific location.

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

public int EndSendTo(
	IAsyncResult asyncResult


Type: System.IAsyncResult

An IAsyncResult that stores state information and any user defined data for this asynchronous operation.

Return Value

Type: System.Int32
If successful, the number of bytes sent; otherwise, an invalid Socket error.


asyncResult is null.


asyncResult was not returned by a call to the BeginSendTo method.


EndSendTo was previously called for the asynchronous send.


An error occurred when attempting to access the socket. See the Remarks section for more information.


The Socket has been closed.

EndSendTo completes the asynchronous send operation started in BeginSendTo.

Before calling BeginSendTo, you need to create a callback method that implements the AsyncCallback delegate. This callback method executes in a separate thread and is called by the system after BeginReceive returns. The callback method must accept the IAsyncResult returned by the BeginSendTo method as a parameter.

Within the callback method, call the AsyncState method of the IAsyncResult parameter to obtain the sending Socket. After obtaining the Socket, you can call the EndSendTo method to successfully complete the send operation and return the number of bytes sent.

If you are using a connectionless protocol, EndSendTo will block until the datagram is sent. If you are using a connection-oriented protocol, EndSendTo will block until the requested number of bytes are sent. There is no guarantee that the data you send will appear on the network immediately. To increase network efficiency, the underlying system may delay transmission until a significant amount of outgoing data is collected. A successful completion of the BeginSendTo method means that the underlying system has had room to buffer your data for a network send.


If you receive a SocketException, use the SocketException.ErrorCode property to obtain the specific error code. After you have obtained this code, refer to the Windows Sockets version 2 API error code documentation in the MSDN library for a detailed description of the error.


This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing.

The following code example ends an asynchronous send to a specific location.

	StateObject so = (StateObject) ar.AsyncState;
	Socket s = so.workSocket;

	int send = s.EndSendTo(ar);

       Console.WriteLine("The size of the message sent was :" + send.ToString());
StateObject* so = __try_cast<StateObject*>(ar->AsyncState);
Socket* s = so->workSocket;

int send = s->EndSendTo(ar);

Console::WriteLine(S"The size of the message sent was : {0}", __box(send));


Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

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

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0