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Socket.BeginReceive Method (Byte(), Int32, Int32, SocketFlags, AsyncCallback, Object)

Begins to asynchronously receive data from a connected Socket.

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

<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)> _
Public Function BeginReceive ( _
	buffer As Byte(), _
	offset As Integer, _
	size As Integer, _
	socketFlags As SocketFlags, _
	callback As AsyncCallback, _
	state As Object _
) As IAsyncResult
Dim instance As Socket 
Dim buffer As Byte()
Dim offset As Integer 
Dim size As Integer 
Dim socketFlags As SocketFlags 
Dim callback As AsyncCallback 
Dim state As Object 
Dim returnValue As IAsyncResult 

returnValue = instance.BeginReceive(buffer, _
	offset, size, socketFlags, callback, _


Type: System.Byte()

An array of type Byte that is the storage location for the received data.

Type: System.Int32

The zero-based position in the buffer parameter at which to store the received data.

Type: System.Int32

The number of bytes to receive.

Type: System.Net.Sockets.SocketFlags

A bitwise combination of the SocketFlags values.

Type: System.AsyncCallback

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

Type: System.Object

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

Return Value

Type: System.IAsyncResult
An IAsyncResult that references the asynchronous read.


buffer is Nothing.


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


Socket has been closed.


offset is less than 0.


offset is greater than the length of buffer.


size is less than 0.


size is greater than the length of buffer minus the value of the offset parameter.


The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

The asynchronous BeginReceive operation must be completed by calling the EndReceive method. Typically, the method is invoked by the callback delegate.

This method does not block until the operation is complete. To block until the operation is complete, use one of the Receive method overloads.

To cancel a pending BeginReceive, call the Close method.

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.


All I/O initiated by a given thread is canceled when that thread exits. A pending asynchronous operation can fail if the thread exits before the operation completes.


state is an instantiation of a user-defined class.


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


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 begins to asynchronously receive data from a connected Socket.

Public Class StateObject
   Public workSocket As Socket = Nothing 
   Public const BUFFER_SIZE As Integer = 1024
   Public buffer(BUFFER_SIZE) As byte
   Public sb As New StringBuilder()
End Class 'StateObject
__gc public class StateObject {
    static const int BUFFER_SIZE = 1024;
    Socket* workSocket;
    Byte buffer[];
    StringBuilder* sb;

    StateObject() : workSocket(0) {
        buffer = new Byte[BUFFER_SIZE];
        sb = new StringBuilder();
Public Shared Sub Listen_Callback(ar As IAsyncResult)
   Dim s As Socket = CType(ar.AsyncState, Socket)
   Dim s2 As Socket = s.EndAccept(ar)
   Dim so2 As New StateObject()
   so2.workSocket = s2
   s2.BeginReceive(so2.buffer, 0, StateObject.BUFFER_SIZE, 0, New AsyncCallback(AddressOf Async_Send_Receive.Read_Callback), so2)
End Sub 'Listen_Callback
static void Listen_Callback(IAsyncResult* ar) {
    Socket* s = __try_cast<Socket*>(ar->AsyncState);
    Socket* s2 = s->EndAccept(ar);
    StateObject* so2 = new StateObject();
    so2->workSocket = s2;
    s2->BeginReceive(so2->buffer, 0, StateObject::BUFFER_SIZE, SocketFlags::None,
        new AsyncCallback(0, &Async_Send_Receive::Read_Callback), so2);    
Public Shared Sub Read_Callback(ar As IAsyncResult)
   Dim so As StateObject = CType(ar.AsyncState, StateObject)
   Dim s As Socket = so.workSocket

   Dim read As Integer = s.EndReceive(ar)

   If read > 0 Then, 0, read))
      s.BeginReceive(so.buffer, 0, StateObject.BUFFER_SIZE, 0, New AsyncCallback(AddressOf Async_Send_Receive.Read_Callback), so)
      If > 1 Then 
         'All the data has been read, so displays it to the console 
         Dim strContent As String
         strContent =
         Console.WriteLine([String].Format("Read {0} byte from socket" + "data = {1} ", strContent.Length, strContent))
      End If
   End If 
End Sub 'Read_Callback
static void Read_Callback(IAsyncResult* ar){
    StateObject* so = __try_cast<StateObject*>(ar->AsyncState);
    Socket* s = so->workSocket;

    int read = s->EndReceive(ar);

    if (read > 0) {
        so->sb->Append(Encoding::ASCII->GetString(so->buffer, 0, read));
        s->BeginReceive(so->buffer, 0, StateObject::BUFFER_SIZE, SocketFlags::None, 
            new AsyncCallback(0, &Async_Send_Receive::Read_Callback), so);
    } else {
        if (so->sb->Length > 1) {
            //All of the data has been read, so displays it to the console
            String* strContent = so->sb->ToString();
            Console::WriteLine(String::Format(S"Read {0} byte from socket data = {1} ",
                __box(strContent->Length), strContent));

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