Export (0) Print
Expand All

Socket.Connect Method (EndPoint)

Establishes a connection to a remote host.

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

'Declaration
Public Sub Connect ( _
	remoteEP As EndPoint _
)

Parameters

remoteEP
Type: System.Net.EndPoint

An EndPoint that represents the remote device.

ExceptionCondition
ArgumentNullException

remoteEP is Nothing.

SocketException

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

ObjectDisposedException

The Socket has been closed.

SecurityException

A caller higher in the call stack does not have permission for the requested operation.

InvalidOperationException

The Socket is Listening.

If you are using a connection-oriented protocol such as TCP, the Connect method synchronously establishes a network connection between LocalEndPoint and the specified remote endpoint. If you are using a connectionless protocol, Connect establishes a default remote host. After you call Connect, you can send data to the remote device with the Send method, or receive data from the remote device with the Receive method.

If you are using a connectionless protocol such as UDP, you do not have to call Connect before sending and receiving data. You can use SendTo and ReceiveFrom to synchronously communicate with a remote host. If you do call Connect, any datagrams that arrive from an address other than the specified default will be discarded. If you want to set your default remote host to a broadcast address, you must first call the SetSocketOption method and set the socket option to SocketOptionName.Broadcast, or Connect 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.

The Connect method will block, unless you specifically set the Blocking property to false prior to calling Connect. If you are using a connection-oriented protocol like TCP and you do disable blocking, Connect will throw a SocketException because it needs time to make the connection. Connectionless protocols will not throw an exception because they simply establish a default remote host. You can use SocketException.ErrorCode 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. If the error returned WSAEWOULDBLOCK, the remote host connection has been initiated by a connection-oriented Socket, but has not yet completed successfully. Use the Poll method to determine when the Socket is finished connecting.

NoteNote

If you are using a connection-oriented protocol and did not call Bind before calling Connect, the underlying service provider will assign the local network address and port number. If you are using a connectionless protocol, the service provider will not assign a local network address and port number until you complete a send or receive operation. If you want to change the default remote host, call Connect again with the desired endpoint.

NoteNote

If the socket has been previously disconnected, then you cannot use this method to restore the connection. Use one of the asynchronous BeginConnect methods to reconnect. This is a limitation of the underlying provider.

NoteNote

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 connects to a remote endpoint and then verifies the connection.

    ' .Connect throws an exception if unsuccessful
    client.Connect(anEndPoint)

    ' This is how you can determine whether a socket is still connected. 
    Dim blockingState As Boolean = client.Blocking
    Try 
        Dim tmp(0) As Byte

        client.Blocking = False
        client.Send(tmp, 0, 0)
        Console.WriteLine("Connected!")
    Catch e As SocketException
        ' 10035 == WSAEWOULDBLOCK 
        If e.NativeErrorCode.Equals(10035) Then
            Console.WriteLine("Still Connected, but the Send would block")
        Else
            Console.WriteLine("Disconnected: error code {0}!", e.NativeErrorCode)
        End If 
    Finally
        client.Blocking = blockingState
    End Try

    Console.WriteLine("Connected: {0}", client.Connected)

End Sub 'ConnectAndCheck

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Show:
© 2015 Microsoft