CAsyncSocket::GetSockOpt

Call this member function to retrieve a socket option.

BOOL GetSockOpt(
   int nOptionName,
   void* lpOptionValue,
   int* lpOptionLen,
   int nLevel = SOL_SOCKET 
);

Parameters

• nOptionName
  The socket option for which the value is to be retrieved.

• lpOptionValue
  A pointer to the buffer in which the value for the requested option is to be returned. The value associated with the selected option is returned in the buffer lpOptionValue. The integer pointed to by lpOptionLen should originally contain the size of this buffer in bytes; and on return, it will be set to the size of the value returned. For SO_LINGER, this will be the size of a LINGER structure; for all other options it will be the size of a BOOL or an int, depending on the option. See the list of options and their sizes in the Remarks section.

• lpOptionLen
  A pointer to the size of the lpOptionValue buffer in bytes.

• nLevel
  The level at which the option is defined; the only supported levels are SOL_SOCKET and IPPROTO_TCP.

Return Value

Nonzero if the function is successful; otherwise 0, and a specific error code can be retrieved by calling GetLastError. If an option was never set with SetSockOpt, then GetSockOpt returns the default value for the option. 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.

• WSAEFAULT   The lpOptionLen argument was invalid.

• WSAEINPROGRESS   A blocking Windows Sockets operation is in progress.

• WSAENOPROTOOPT   The option is unknown or unsupported. In particular, SO_BROADCAST is not supported on sockets of type SOCK_STREAM, while SO_ACCEPTCONN, SO_DONTLINGER, SO_KEEPALIVE, SO_LINGER, and SO_OOBINLINE are not supported on sockets of type SOCK_DGRAM.

• WSAENOTSOCK   The descriptor is not a socket.

Remarks

GetSockOpt retrieves the current value for a socket option associated with a socket of any type, in any state, and stores the result in lpOptionValue. Options affect socket operations, such as the routing of packets, out-of-band data transfer, and so on.

The following options are supported for GetSockOpt. The Type identifies the type of data addressed by lpOptionValue. The TCP_NODELAY option uses level IPPROTO_TCP; all other options use level SOL_SOCKET.

Value	Type	Meaning
SO_ACCEPTCONN	BOOL	Socket is listening.
SO_BROADCAST	BOOL	Socket is configured for the transmission of broadcast messages.
SO_DEBUG	BOOL	Debugging is enabled.
SO_DONTLINGER	BOOL	If true, the SO_LINGER option is disabled.
SO_DONTROUTE	BOOL	Routing is disabled.
SO_ERROR	int	Retrieve error status and clear.
SO_KEEPALIVE	BOOL	Keep-alives are being sent.
SO_LINGER	struct LINGER	Returns the current linger options.
SO_OOBINLINE	BOOL	Out-of-band data is being received in the normal data stream.
SO_RCVBUF	int	Buffer size for receives.
SO_REUSEADDR	BOOL	The socket can be bound to an address which is already in use.
SO_SNDBUF	int	Buffer size for sends.
SO_TYPE	int	The type of the socket (for example, SOCK_STREAM).
TCP_NODELAY	BOOL	Disables the Nagle algorithm for send coalescing.

Berkeley Software Distribution (BSD) options not supported for GetSockOpt are:

Value	Type	Meaning
SO_RCVLOWAT	int	Receive low water mark.
SO_RCVTIMEO	int	Receive timeout.
SO_SNDLOWAT	int	Send low water mark.
SO_SNDTIMEO	int	Send timeout.
IP_OPTIONS		Get options in IP header.
TCP_MAXSEG	int	Get TCP maximum segment size.

Calling GetSockOpt with an unsupported option will result in an error code of WSAENOPROTOOPT being returned from GetLastError.

Requirements

Header: afxsock.h

See Also

Reference

CAsyncSocket Class

Hierarchy Chart

CAsyncSocket::SetSockOpt

Other Resources

CAsyncSocket Members