Socket.SendTo Method (Byte(), Int32, SocketFlags, EndPoint)


Sends the specified number of bytes of data to the specified endpoint using the specified SocketFlags.

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

Public Function SendTo (
	buffer As Byte(),
	size As Integer,
	socketFlags As SocketFlags,
	remoteEP As EndPoint
) As Integer


Type: System.Byte()

An array of type Byte that contains the data to be sent.

Type: System.Int32

The number of bytes to send.

Type: System.Net.Sockets.SocketFlags

A bitwise combination of the SocketFlags values.

Type: System.Net.EndPoint

The EndPoint that represents the destination location for the data.

Return Value

Type: System.Int32

The number of bytes sent.

Exception Condition

buffer is null.


remoteEP is null.


The specified size exceeds the size of buffer.


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


The Socket has been closed.

In this overload, the buffer offset defaults to 0. If you specify the DontRoute flag as the socketflags parameter, the data you are sending will not be routed.

If you are using a connectionless protocol, you do not need to establish a default remote host with the Connect method prior to calling SendTo. You only need to do this if you intend to call the Send method. If you do call the Connect method prior to calling SendTo, the remoteEP parameter will override the specified default remote host for that send operation only. You are also not required to call the Bind method, because the underlying service provider will assign the most appropriate local network address and port number. If you need to identify the assigned local network address and port number, you can use the LocalEndPoint property after the SendTo method successfully completes.

Although intended for connectionless protocols, SendTo also works with connection-oriented protocols. If you are using a connection-oriented protocol, you must first establish a remote host connection by calling the Connect method or accept an incoming connection request using the Accept method. If you do not establish or accept a remote host connection, SendTo will throw a SocketException. You can also establish a default remote host for a connectionless protocol prior to calling the SendTo method. In either of these cases, SendTo will ignore the remoteEP parameter and only send data to the connected or default remote host.

Blocking sockets will block until the requested number of bytes are sent. Since a nonblockingSocket completes immediately, it might not send all of the bytes requested in a single operation. It is your application's responsibility to keep track of the number of bytes sent and to retry the operation until the application sends the requested number of bytes. There is also 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 out-going data is collected. A successful completion of the SendTo method means that the underlying system has had room to buffer your data for a network send.

If you are using a connectionless protocol in blocking mode, SendTo will block until the datagram is sent. If you want to send data to a broadcast address, you must first call the SetSocketOption method and set the socket option to SocketOptionName.Broadcast. You must also be sure that the number of bytes sent does not exceed the maximum packet size of the underlying service provider. If it does, the datagram will not be sent and SendTo will throw a SocketException.


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 in the .NET Framework.

The following code example sends a connectionless datagram to the specified remote host. The size and SocketFlags are passed to the SendTo method.

Public Shared Sub SendTo3() 
    Dim hostEntry As IPHostEntry = Dns.GetHostEntry(Dns.GetHostName())
    Dim endPoint As New IPEndPoint(hostEntry.AddressList(0), 11000)

    Dim s As New Socket(endPoint.Address.AddressFamily, SocketType.Dgram, ProtocolType.Udp)

    Dim msg As Byte() = Encoding.ASCII.GetBytes("This is a test")
    Console.WriteLine("Sending data.")
    ' This call blocks. 
    s.SendTo(msg, msg.Length, SocketFlags.None, endPoint)

End Sub 'SendTo3

.NET Framework
Available since 1.1
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