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


The .NET API Reference documentation has a new home. Visit the .NET API Browser on to see the new experience.

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.

Exception Condition

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 in the .NET Framework.

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);



to execute unmanaged code. Associated enumeration: UnmanagedCode.

.NET Framework
Available since 1.1
Return to top