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Socket.IOControl Method (IOControlCode, Byte[], Byte[])

Sets low-level operating modes for the Socket using the IOControlCode enumeration to specify control codes.

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

public int IOControl(
	IOControlCode ioControlCode,
	byte[] optionInValue,
	byte[] optionOutValue


Type: System.Net.Sockets.IOControlCode

A IOControlCode value that specifies the control code of the operation to perform.

Type: System.Byte[]

An array of type Byte that contains the input data required by the operation.

Type: System.Byte[]

An array of type Byte that contains the output data returned by the operation.

Return Value

Type: System.Int32
The number of bytes in the optionOutValue parameter.


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


The Socket has been closed.


An attempt was made to change the blocking mode without using the Blocking property.

This method provides low-level access to the operating system Socket underlying the current instance of the Socket class. For more, see the WSAIoctl documentation in the MSDN library.


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 compares the results of calling IOControl with DataToRead and the Available property.

static void DisplayPendingByteCount(Socket s)
    byte[] outValue = BitConverter.GetBytes(0);

    // Check how many bytes have been received.
    s.IOControl(IOControlCode.DataToRead, null, outValue);

    uint bytesAvailable = BitConverter.ToUInt32(outValue, 0);
    Console.Write("server has {0} bytes pending. ", 
    Console.WriteLine("Available property says {1}.",

void DisplayPendingByteCount(Socket* s)
    Byte outValue[] = BitConverter::GetBytes(0);

    // Check how many bytes have been received.
    s->IOControl(IOControlCode::DataToRead, 0, outValue);

    UInt32 bytesAvailable = BitConverter::ToUInt32(outValue, 0);
    Console::Write(S"server has {0} bytes pending,",  
    Console::WriteLine(S"Available property says {1}.", 


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

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