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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 int SendTo(
	byte[] buffer,
	int size,
	SocketFlags socketFlags,
	EndPoint remoteEP


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.


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 nonblocking Socket 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.

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

public static void SendTo3()
    IPHostEntry hostEntry = Dns.GetHostEntry(Dns.GetHostName());
    IPEndPoint endPoint = new IPEndPoint(hostEntry.AddressList[0], 11000);

    Socket s = new Socket(endPoint.Address.AddressFamily,

    byte[] msg = Encoding.ASCII.GetBytes("This is a test");
    Console.WriteLine("Sending data.");
    // This call blocks. 
    s.SendTo(msg, msg.Length, SocketFlags.None, endPoint);
static void SendTo3()
    IPHostEntry* hostEntry = Dns::Resolve(Dns::GetHostName());
    IPEndPoint* endPoint = new IPEndPoint(hostEntry->AddressList[0], 11000);

    Socket* s = new Socket(endPoint->Address->AddressFamily,

    Byte msg[]= Encoding::ASCII->GetBytes(S"This is a test");
    Console::WriteLine(S"Sending data.");
    // This call blocks. 
    s->SendTo(msg, msg->Length, SocketFlags::None, endPoint);

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