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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