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Socket.IOControl Method (Int32, Byte[], Byte[])

Sets low-level operating modes for the Socket using numerical control codes.

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

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


Type: System.Int32

An Int32 value that specifies the control code of the operation to perform.

Type: System.Byte[]

A Byte array that contains the input data required by the operation.

Type: System.Byte[]

A Byte array 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.


A caller in the call stack does not have the required permissions.

The IOControl method provides low-level access to the operating system Socket underlying the current instance of the Socket class. For more information, 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 FIONREAD and the Available property.

// FIONREAD is also available as the "Available" property.
public const int FIONREAD   = 0x4004667F;

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

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

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

// FIONREAD is also available as the "Available" property.
const int FIONREAD   = 0x4004667F;

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

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

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


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