CAsyncSocket::SendTo

int SendTo( const void* lpBuf, int nBufLen, UINT nHostPort, LPCTSTR lpszHostAddress = NULL, int nFlags = 0 );

int SendTo( const void* lpBuf, int nBufLen, const SOCKADDR* lpSockAddr, int nSockAddrLen, int nFlags = 0 );

Return Value

If no error occurs, SendTo returns the total number of characters sent. (Note that this can be less than the number indicated by nBufLen.) 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.
WSAEACCES The requested address is a broadcast address, but the appropriate flag was not set.
WSAEINPROGRESS A blocking Windows Sockets operation is in progress.
WSAEFAULT The lpBuf or lpSockAddr parameters are not part of the user address space, or the lpSockAddr argument is too small (less than the size of a SOCKADDR structure).
WSAEINVAL The host name is invalid.
WSAENETRESET The connection must be reset because the Windows Sockets implementation dropped it.
WSAENOBUFS The Windows Sockets implementation reports a buffer deadlock.
WSAENOTCONN The socket is not connected (SOCK_STREAM only).
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 SendTo on a socket after ShutDown has been invoked with nHow set to 1 or 2.
WSAEWOULDBLOCK The socket is marked as nonblocking and the requested operation would block.
WSAEMSGSIZE The socket is of type SOCK_DGRAM, and the datagram is larger than the maximum supported by the Windows Sockets implementation.
WSAECONNABORTED The virtual circuit was aborted due to timeout or other failure.
WSAECONNRESET The virtual circuit was reset by the remote side.
WSAEADDRNOTAVAIL The specified address is not available from the local machine.
WSAEAFNOSUPPORT Addresses in the specified family cannot be used with this socket.
WSAEDESTADDRREQ A destination address is required.
WSAENETUNREACH The network cannot be reached from this host at this time.

Parameters

lpBuf

A buffer containing the data to be transmitted.

nBufLen

The length of the data in lpBuf in bytes.

nHostPort

The port identifying the socket application.

lpszHostAddress

The network address of the socket to which this object is connected: a machine name such as “ftp.microsoft.com,” or a dotted number such as “128.56.22.8”.

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_DONTROUTE Specifies that the data should not be subject to routing. A Windows Sockets supplier can choose to ignore this flag; see also the discussion of the SO_DONTROUTE option in Windows Sockets Programming Considerations in the Win32 SDK documentation.
MSG_OOB Send out-of-band data (SOCK_STREAM only).

lpSockAddr

A pointer to a SOCKADDR structure that contains the address of the target socket.

nSockAddrLen

The length of the address in lpSockAddr in bytes.

Remarks

Call this member function to send data to a specific destination. SendTo is used on datagram or stream sockets and is used to write outgoing data on a socket. For datagram sockets, care must be taken not to exceed the maximum IP packet size of the underlying subnets, which is given by the iMaxUdpDg element in the WSADATA structure filled out by AfxSocketInit. If the data is too long to pass atomically through the underlying protocol, the error WSAEMSGSIZE is returned, and no data is transmitted.

Note that the successful completion of a SendTo does not indicate that the data was successfully delivered.

SendTo is only used on a SOCK_DGRAM socket to send a datagram to a specific socket identified by the lpSockAddr parameter.

To send a broadcast (on a SOCK_DGRAM only), the address in the lpSockAddr parameter should be constructed using the special IP address INADDR_BROADCAST (defined in the Windows Sockets header file WINSOCK.H) together with the intended port number. Or, if the lpszHostAddress parameter is NULL, the socket is configured for broadcast. It is generally inadvisable for a broadcast datagram to exceed the size at which fragmentation can occur, which implies that the data portion of the datagram (excluding headers) should not exceed 512 bytes.

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