getsockopt

getsockopt retrieves the value of the specified option for a socket.

Syntax

int getsockopt(
    SOCKET s,
    int level,
    int optname,
    char *optval,
    int *optlen
);

Parameters

s

Socket descriptor of a currently open socket that uses the IP protocol.

level

Network layer. The values for this parameter are defined under setsockopt.

optname

Type of socket information to be returned. Some values for the optname parameter are not supported. See the Remarks section below.

optval

Pointer to a buffer to receive the option value. Its proper length depends on the type of information being returned, as specified in the optname field.

optlen

Size, in bytes, of the buffer at optval. Upon return, it contains the size of the option value retrieved, and ma be less than the value passed in.

Return Value

0 (zero) if the function succeeds, SOCKET_ERROR if the function fails

Use WSAGetLastError to retrieve a specific error code.

Remarks

Some values for the optname parameter are not supported. The following sections list the options, by socket type, that are supported.

 

SOL_SOCKET level options:

• SO_ACCEPTCONN

• SO_RCVBUF
• SO_SNDBUF
• SO_SND_DGRAMS (see Custom RTX64 socket options below)
• SO_RCV_DGRAMS (see Custom RTX64 socket options below)
• SO_BROADCAST
• SO_KEEPALIVE
• SO_LINGER
• SO_REUSEADDR
• SO_OOBINLINE

 

IPPROTO_TCP level options:

• TCP_NODELAY
• TCP_MAXRT
• TCP_PROVIDE_TIMESTAMPS (see Custom RTX64 socket options below)
• TCP_ACKNSEG (see Custom RTX64 socket options below)
• TCP_ACKDELAYTIME (see Custom RTX64 socket options below)

 

IPPROTO_IP level options:

• IP_DONTFRAGMENT
• IP_HDRINCL
• IP_TTL
• IP_TOS
• IP_MULTICAST_IF
• IP_MULTICAST_TTL

 

IPPROTO_IPV6 level options:

• IPV6_HDRINCL
• IPV6_V6ONLY
• IPV6_UNICAST_HOPS
• IPV6_MULTICAST_IF
• IPV6_MULTICAST_HOPS
• IPV6_MULTICAST_LOOP

NOTE: None of the options for the IPPROTO_RM, NSPROTO_IPX, SOL_APPLETALK, and SOL_IRLMP socket types are supported.

Custom RTX64 socket options:

Option	Value	Description
SO_SND_DGRAMS	0x100B	Maximum count of send datagrams on non-TCP socket (default 32)
SO_RCV_DGRAMS	0x100C	Maximum count of receive datagrams on non-TCP socket (default 32)
TCP_PROVIDE_TIMESTAMPS	13	Turn ON/OFF Time stamp (default off)
TCP_ACKDELAYTIME	23	Set ACK delay time - the delay period (in milliseconds) that the stack uses for delayed acknowledgements (ACKs). A value of zero disables delayed ACKs. Data segments are acknowledged immediately. Default value is 200.
TCP_ACKNSEG	24	Turn ON/OFF the Selective Acknowledgments option in the TCP header. Default is ON. This option can only be changed prior to establishing a TCP connection.