setsockopt

setsockopt, and the corresponding getsockopt, can be used to get and set options for a socket. Use getsockopt to determine socket options. Use setsockopt to set socket options. The new value remains until it is modified again. The optval parameter points to a buffer that specifies the option value according to the option name (optname). The optlen parameter indicates the length of buffer pointed to by optval.  It is used in various ways depending on the specific option. In some cases, it is the length of the option value to be set.

Syntax

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

Parameters

s

Socket descriptor.

level

The layer of the network for which the option is targeted:

• SOL_SOCKET (socket interface level)
• IPPROTO_IP (IP network level for IPv4 sockets)
• IPPROTO_IPV6 (IP network level for IPv6 sockets)
• IPPROTO_TCP (TCP transport level).

optname

Socket option based on the value of level. Some values for the optname parameter are not supported. See the Remarks section below.

optval

Pointer to a buffer to where the option value is stored. Its proper length depends on the type of information being set as specified in the optname field.

optlen

Size, in bytes, of the buffer at optval.

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_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_ADD_MEMBERSHIP
• IP_DROP_MEMBERSHIP
• IP_MULTICAST_IF
• IP_MULTICAST_TTL
• IP_ADD_SOURCE_MEMBERSHIP
• IP_DROP_SOURCE_MEMBERSHIP
• IP_BLOCK_SOURCE
• IP_UNBLOCK_SOURCE
• MCAST_JOIN_SOURCE_GROUP
• MCAST_LEAVE_SOURCE_GROUP
• MCAST_BLOCK_SOURCE
• MCAST_UNBLOCK_SOURCE

 

IPPROTO_IPV6 level options:

• IPV6_HDRINCL
• IPV6_V6ONLY
• IPV6_UNICAST_HOPS
• IPV6_MULTICAST_IF
• IPV6_MULTICAST_HOPS
• IPV6_MULTICAST_LOOP
• IPV6_JOIN_GROUP
• IPV6_LEAVE_GROUP
• MCAST_JOIN_SOURCE_GROUP
• MCAST_LEAVE_SOURCE_GROUP
• MCAST_BLOCK_SOURCE
• MCAST_UNBLOCK_SOURCE

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 (default 200ms)
TCP_ACKNSEG	24	Turn ON/OFF Selective Acknolwlegements (default off)