Socket.BeginConnect Method (String, Int32, AsyncCallback, Object)


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Begins an asynchronous request for a remote host connection. The host is specified by a host name and a port number.

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

[<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)>]
member BeginConnect : 
        host:string *
        port:int *
        requestCallback:AsyncCallback *
        state:Object -> IAsyncResult


Type: System.String

The name of the remote host.

Type: System.Int32

The port number of the remote host.

Type: System.AsyncCallback

An AsyncCallback delegate that references the method to invoke when the connect operation is complete.

Type: System.Object

A user-defined object that contains information about the connect operation. This object is passed to the requestCallback delegate when the operation is complete.

Return Value

Type: System.IAsyncResult

An IAsyncResult that references the asynchronous connection.

Exception Condition

host is null.


The Socket has been closed.


This method is valid for sockets in the InterNetwork or InterNetworkV6 families.


The port number is not valid.


The Socket is Listening.

The asynchronous BeginConnect operation must be completed by calling the EndConnect 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 one of the Connect method overloads.

To cancel a pending call to the BeginConnect method, close the Socket. When the Close method is called while an asynchronous operation is in progress, the callback provided to the BeginConnect method is called. A subsequent call to the EndConnect method will throw an ObjectDisposedException to indicate that the operation has been cancelled.

For detailed information about using the asynchronous programming model, see Calling Synchronous Methods Asynchronously


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.


If this socket has previously been disconnected, then BeginConnect must be called on a thread that will not exit until the operation is complete. This is a limitation of the underlying provider. Also the EndPoint that is used must be different.


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


The execution context (the security context, the impersonated user, and the calling context) is cached for the asynchronous Socket methods. After the first use of a particular context (a specific asynchronous Socket method, a specific Socket instance, and a specific callback), subsequent uses of that context will see a performance improvement.

The following code example initiates an asynchronous connection attempt.

No code example is currently available or this language may not be supported.
No code example is currently available or this language may not be supported.

.NET Framework
Available since 2.0
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