Socket::ReceiveFrom Method (array<Byte>, Int32, Int32, SocketFlags, EndPoint%)

Receives the specified number of bytes of data into the specified location of the data buffer, using the specified SocketFlags, and stores the endpoint.

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

public:
int ReceiveFrom(
	array<unsigned char>^ buffer, 
	int offset, 
	int size, 
	SocketFlags socketFlags, 
	EndPoint^% remoteEP
)

Parameters

buffer
Type: array<System::Byte>

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

offset
Type: System::Int32

The position in the buffer parameter to store the received data.

size
Type: System::Int32

The number of bytes to receive.

socketFlags
Type: System.Net.Sockets::SocketFlags

A bitwise combination of the SocketFlags values.

remoteEP
Type: System.Net::EndPoint%

An EndPoint, passed by reference, that represents the remote server.

Return Value

Type: System::Int32
The number of bytes received.

ExceptionCondition
ArgumentNullException

buffer is nullptr.

-or-

remoteEP is nullptr.

ArgumentOutOfRangeException

offset is less than 0.

-or-

offset is greater than the length of buffer.

-or-

size is less than 0.

-or-

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

SocketException

socketFlags is not a valid combination of values.

-or-

The LocalEndPoint property was not set.

-or-

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

ObjectDisposedException

The Socket has been closed.

The ReceiveFrom method reads data into the buffer parameter, returns the number of bytes successfully read, and captures the remote host endpoint from which the data was sent. This method is useful if you intend to receive connectionless datagrams from an unknown host or multiple hosts.

With connectionless protocols, ReceiveFrom will read the first enqueued datagram received into the local network buffer. If the datagram you receive is larger than the size of buffer, the ReceiveFrom method will fill buffer with as much of the message as is possible, and throw a SocketException. If you are using an unreliable protocol, the excess data will be lost. If you are using a reliable protocol, the excess data will be retained by the service provider and you can retrieve it by calling the ReceiveFrom method with a large enough buffer.

If no data is available for reading, the ReceiveFrom method will block until data is available. If you are in non-blocking mode, and there is no data available in the in the protocol stack buffer, the ReceiveFrom method will complete immediately and throw a SocketException. You can use the Available property to determine if data is available for reading. When Available is non-zero, retry the receive operation.

Although ReceiveFrom is intended for connectionless protocols, you can use a connection-oriented protocol as well. If you choose to do so, you must first either establish a remote host connection by calling the Connect method or accept an incoming remote host connection by calling the Accept method. If you do not establish or accept a connection before calling the ReceiveFrom method, you will get a SocketException. You can also establish a default remote host for a connectionless protocol prior to calling the ReceiveFrom method. In either of these cases, the ReceiveFrom method will ignore the remoteEP parameter and only receive data from the connected or default remote host.

With connection-oriented sockets, ReceiveFrom will read as much data as is available up to the amount of bytes specified by the size parameter. If the remote host shuts down the Socket connection with the Shutdown method, and all available data has been Received, the ReceiveFrom method will complete immediately and return zero bytes.

NoteNote

Before calling ReceiveFrom, you must explicitly bind the Socket to a local endpoint using the Bind method. If you do not, ReceiveFrom will throw a SocketException. 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.

NoteNote

The AddressFamily of the EndPoint used in ReceiveFrom needs to match the AddressFamily of the EndPoint used in SendTo.

NoteNote

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 receives a connectionless datagram from a remote host. The offset, buffer size, and SocketFlags are passed to the ReceiveFrom method.

static void ReceiveFrom4()
{
   IPHostEntry^ hostEntry = Dns::Resolve( Dns::GetHostName() );
   IPEndPoint^ endPoint = gcnew IPEndPoint( hostEntry->AddressList[ 0 ],11000 );

   Socket^ s = gcnew Socket( endPoint->Address->AddressFamily,
      SocketType::Dgram,
      ProtocolType::Udp );

   // Creates an IpEndPoint to capture the identity of the sending host.
   IPEndPoint^ sender = gcnew IPEndPoint( IPAddress::Any,0 );
   EndPoint^ senderRemote = safe_cast<EndPoint^>(sender);

   // Binding is required with ReceiveFrom calls.
   s->Bind( endPoint );

   array<Byte>^ msg = gcnew array<Byte>(256);
   Console::WriteLine(  "SWaiting to receive datagrams from client..." );
   // This call blocks.  
   s->ReceiveFrom( msg, 0, msg->Length, SocketFlags::None, senderRemote );
   s->Close();
}

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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