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CAsyncSocket::Receive 

Call this member function to receive data from a socket.


virtual int Receive(
   void* lpBuf,
   int nBufLen,
   int nFlags = 0 
);

Parameters

lpBuf

A buffer for the incoming data.

nBufLen

The length of lpBuf in bytes.

nFlags

Specifies the way in which the call is made. The semantics of this function are determined by the socket options and the nFlags parameter. The latter is constructed by combining any of the following values with the C++ OR operator:

  • MSG_PEEK   Peek at the incoming data. The data is copied into the buffer but is not removed from the input queue.

  • MSG_OOB   Process out-of-band data.

If no error occurs, Receive returns the number of bytes received. If the connection has been closed, it returns 0. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling GetLastError. The following errors apply to this member function:

  • WSANOTINITIALISED   A successful AfxSocketInit must occur before using this API.

  • WSAENETDOWN   The Windows Sockets implementation detected that the network subsystem failed.

  • WSAENOTCONN   The socket is not connected.

  • WSAEINPROGRESS   A blocking Windows Sockets operation is in progress.

  • WSAENOTSOCK   The descriptor is not a socket.

  • WSAEOPNOTSUPP   MSG_OOB was specified, but the socket is not of type SOCK_STREAM.

  • WSAESHUTDOWN   The socket has been shut down; it is not possible to call Receive on a socket after ShutDown has been invoked with nHow set to 0 or 2.

  • WSAEWOULDBLOCK   The socket is marked as nonblocking and the Receive operation would block.

  • WSAEMSGSIZE   The datagram was too large to fit into the specified buffer and was truncated.

  • WSAEINVAL   The socket has not been bound with Bind.

  • WSAECONNABORTED   The virtual circuit was aborted due to timeout or other failure.

  • WSAECONNRESET   The virtual circuit was reset by the remote side.

This function is used for connected stream or datagram sockets and is used to read incoming data.

For sockets of type SOCK_STREAM, as much information as is currently available up to the size of the buffer supplied is returned. If the socket has been configured for in-line reception of out-of-band data (socket option SO_OOBINLINE) and out-of-band data is unread, only out-of-band data will be returned. The application can use the IOCtl SIOCATMARK option or OnOutOfBandData to determine whether any more out-of-band data remains to be read.

For datagram sockets, data is extracted from the first enqueued datagram, up to the size of the buffer supplied. If the datagram is larger than the buffer supplied, the buffer is filled with the first part of the datagram, the excess data is lost, and Receive returns a value of SOCKET_ERROR with the error code set to WSAEMSGSIZE. If no incoming data is available at the socket, a value of SOCKET_ERROR is returned with the error code set to WSAEWOULDBLOCK. The OnReceive callback function can be used to determine when more data arrives.

If the socket is of type SOCK_STREAM and the remote side has shut down the connection gracefully, a Receive will complete immediately with 0 bytes received. If the connection has been reset, a Receive will fail with the error WSAECONNRESET.

Receive should be called only once for each time CAsyncSocket::OnReceive is called.

See the example for CAsyncSocket::OnReceive.

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