setsockopt
The setsockopt function sets a socket option.int setsockopt(
SOCKET s,
int level,
int optname,
const char* optval,
int optlen
);Parameters
s
[in] Descriptor identifying a socket.
level
[in] Level at which the option is defined. Example: SOL_SOCKET.
optname
[in] Socket option for which the value is to be set. Example: SO_BROADCAST. The optname value must be a socket option defined within the specified level, or behavior is undefined.
optval
[in] Pointer to the buffer in which the value for the requested option is specified.
optlen
[in] Size of the optval buffer, in bytes.
Return Values
If no error occurs, setsockopt returns zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError.Error code Meaning
WSANOTINITIALISED A successful WSAStartup call must occur before using this function.
WSAENETDOWN The network subsystem has failed.
WSAEFAULT optval is not in a valid part of the process address space or optlen parameter is too small.
WSAEINPROGRESS A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.
WSAEINVAL level is not valid, or the information in optval is not valid.
WSAENETRESET Connection has timed out when SO_KEEPALIVE is set.
WSAENOPROTOOPT The option is unknown or unsupported for the specified provider or socket (see SO_GROUP_PRIORITY limitations).
WSAENOTCONN Connection has been reset when SO_KEEPALIVE is set.
WSAENOTSOCK The descriptor is not a socket.
Res
The setsockopt function sets the current value for a socket option associated with a socket of any type, in any state. Although options can exist at multiple protocol levels, they are always present at the uppermost socket level. Options affect socket operations, such as whether expedited data (OOB data for example) is received in the normal data stream, and whether broadcast messages can be sent on the socket.Note If the setsockopt function is called before the bind function, TCP/IP options will not be checked with TCP/IP until the bind occurs. In this case, the setsockopt function call will always succeed, but the bind function call may fail because of an early setsockopt failing.Note If a socket is opened, a setsockopt call is made, and then a sendto call is made, Windows Sockets performs an implicit bind function call.There are two types of socket options: Boolean options that enable or disable a feature or behavior, and options that require an integer value or structure. To enable a Boolean option, optval points to a nonzero integer. To disable the option optval points to an integer equal to zero. The optlen parameter should be equal to sizeof(int) for Boolean options. For other options, optval points to the an integer or structure that contains the desired value for the option, and optlen is the length of the integer or structure.The following options are supported for setsockopt. For default values of these options, see the description. The Type identifies the type of data addressed by optval.For more information on socket options, see Socket Options.level = SOL_SOCKETValue Type Meaning
SO_BROADCAST BOOL Enables transmission and receipt of broadcast messages on the socket.
SO_CONDITIONAL_ACCEPT BOOL Enables sockets to delay the acknowledgment of a connection until after the WSAAccept condition function is called.
SO_DEBUG BOOL Records debugging information.
SO_DONTLINGER BOOL Does not block close waiting for unsent data to be sent. Setting this option is equivalent to setting SO_LINGER with l_onoff set to zero.
SO_DONTROUTE BOOL Does not route: sends directly to interface. Succeeds but is ignored on AF_INET sockets; fails on AF_INET6 sockets with WSAENOPROTOOPT. Not supported on ATM sockets (results in an error).
SO_GROUP_PRIORITY int Reserved.
SO_KEEPALIVE BOOL Sends keep-alives. Not supported on ATM sockets (results in an error).
SO_LINGER LINGER Lingers on close if unsent data is present.
SO_OOBINLINE BOOL Receives OOB data in the normal data stream. (See section Protocol Independent Out-Of-band Data for a discussion of this topic.)
SO_RCVBUF int Specifies the total per-socket buffer space reserved for receives. This is unrelated to SO_MAX_MSG_SIZE or the size of a TCP window.
SO_REUSEADDR BOOL Allows the socket to be bound to an address that is already in use. (See bind.) Not applicable on ATM sockets.
SO_EXCLUSIVEADDRUSE BOOL Enables a socket to be bound for exclusive access. Does not require administrative privilege.
SO_SNDBUF int Specifies the total per-socket buffer space reserved for sends. This is unrelated to SO_MAX_MSG_SIZE or the size of a TCP window.
PVD_CONFIG Service Provider Dependent This object stores the configuration information for the service provider associated with socket s. The exact format of this data structure is service provider specific. level = IPPROTO_TCP1Value Type Meaning
TCP_NODELAY BOOL Disables the Nagle algorithm for send coalescing.
1 included for backward compatibility with Windows Sockets 1.1 level = NSPROTO_IPXNote Windows NT supports all IPX options. Windows Me/98/95 support only the following options:Note IPX_PTYPE
IPX_FILTERPTYPE
IPX_DSTYPE
IPX_RECVHDR
IPX_MAXSIZE (used with the getsockopt function)
IPX_ADDRESS (used with the getsockopt function)Value Type Meaning
IPX_PTYPE int Sets the IPX packet type.
IPX_FILTERPTYPE int Sets the receive filter packet type
IPX_STOPFILTERPTYPE int Stops filtering the filter type set with IPX_FILTERTYPE
IPX_DSTYPE int Sets the value of the data stream field in the SPX header on every packet sent.
IPX_EXTENDED_ADDRESS BOOL Sets whether extended addressing is enabled.
IPX_RECVHDR BOOL Sets whether the protocol header is sent up on all receive headers.
IPX_RECEIVE_BROADCAST BOOL Indicates broadcast packets are likely on the socket. Set to TRUE by default. Applications that do not use broadcasts should set this to FALSE for better system performance.
IPX_IMMEDIATESPXACK BOOL Directs SPX connections not to delay before sending an ACK. Applications without back-and-forth traffic should set this to TRUE to increase performance.
The setsockopt function sets a socket option.int setsockopt(
SOCKET s,
int level,
int optname,
const char* optval,
int optlen
);Parameters
s
[in] Descriptor identifying a socket.
level
[in] Level at which the option is defined. Example: SOL_SOCKET.
optname
[in] Socket option for which the value is to be set. Example: SO_BROADCAST. The optname value must be a socket option defined within the specified level, or behavior is undefined.
optval
[in] Pointer to the buffer in which the value for the requested option is specified.
optlen
[in] Size of the optval buffer, in bytes.
Return Values
If no error occurs, setsockopt returns zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError.Error code Meaning
WSANOTINITIALISED A successful WSAStartup call must occur before using this function.
WSAENETDOWN The network subsystem has failed.
WSAEFAULT optval is not in a valid part of the process address space or optlen parameter is too small.
WSAEINPROGRESS A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.
WSAEINVAL level is not valid, or the information in optval is not valid.
WSAENETRESET Connection has timed out when SO_KEEPALIVE is set.
WSAENOPROTOOPT The option is unknown or unsupported for the specified provider or socket (see SO_GROUP_PRIORITY limitations).
WSAENOTCONN Connection has been reset when SO_KEEPALIVE is set.
WSAENOTSOCK The descriptor is not a socket.
Res
The setsockopt function sets the current value for a socket option associated with a socket of any type, in any state. Although options can exist at multiple protocol levels, they are always present at the uppermost socket level. Options affect socket operations, such as whether expedited data (OOB data for example) is received in the normal data stream, and whether broadcast messages can be sent on the socket.Note If the setsockopt function is called before the bind function, TCP/IP options will not be checked with TCP/IP until the bind occurs. In this case, the setsockopt function call will always succeed, but the bind function call may fail because of an early setsockopt failing.Note If a socket is opened, a setsockopt call is made, and then a sendto call is made, Windows Sockets performs an implicit bind function call.There are two types of socket options: Boolean options that enable or disable a feature or behavior, and options that require an integer value or structure. To enable a Boolean option, optval points to a nonzero integer. To disable the option optval points to an integer equal to zero. The optlen parameter should be equal to sizeof(int) for Boolean options. For other options, optval points to the an integer or structure that contains the desired value for the option, and optlen is the length of the integer or structure.The following options are supported for setsockopt. For default values of these options, see the description. The Type identifies the type of data addressed by optval.For more information on socket options, see Socket Options.level = SOL_SOCKETValue Type Meaning
SO_BROADCAST BOOL Enables transmission and receipt of broadcast messages on the socket.
SO_CONDITIONAL_ACCEPT BOOL Enables sockets to delay the acknowledgment of a connection until after the WSAAccept condition function is called.
SO_DEBUG BOOL Records debugging information.
SO_DONTLINGER BOOL Does not block close waiting for unsent data to be sent. Setting this option is equivalent to setting SO_LINGER with l_onoff set to zero.
SO_DONTROUTE BOOL Does not route: sends directly to interface. Succeeds but is ignored on AF_INET sockets; fails on AF_INET6 sockets with WSAENOPROTOOPT. Not supported on ATM sockets (results in an error).
SO_GROUP_PRIORITY int Reserved.
SO_KEEPALIVE BOOL Sends keep-alives. Not supported on ATM sockets (results in an error).
SO_LINGER LINGER Lingers on close if unsent data is present.
SO_OOBINLINE BOOL Receives OOB data in the normal data stream. (See section Protocol Independent Out-Of-band Data for a discussion of this topic.)
SO_RCVBUF int Specifies the total per-socket buffer space reserved for receives. This is unrelated to SO_MAX_MSG_SIZE or the size of a TCP window.
SO_REUSEADDR BOOL Allows the socket to be bound to an address that is already in use. (See bind.) Not applicable on ATM sockets.
SO_EXCLUSIVEADDRUSE BOOL Enables a socket to be bound for exclusive access. Does not require administrative privilege.
SO_SNDBUF int Specifies the total per-socket buffer space reserved for sends. This is unrelated to SO_MAX_MSG_SIZE or the size of a TCP window.
PVD_CONFIG Service Provider Dependent This object stores the configuration information for the service provider associated with socket s. The exact format of this data structure is service provider specific. level = IPPROTO_TCP1Value Type Meaning
TCP_NODELAY BOOL Disables the Nagle algorithm for send coalescing.
1 included for backward compatibility with Windows Sockets 1.1 level = NSPROTO_IPXNote Windows NT supports all IPX options. Windows Me/98/95 support only the following options:Note IPX_PTYPE
IPX_FILTERPTYPE
IPX_DSTYPE
IPX_RECVHDR
IPX_MAXSIZE (used with the getsockopt function)
IPX_ADDRESS (used with the getsockopt function)Value Type Meaning
IPX_PTYPE int Sets the IPX packet type.
IPX_FILTERPTYPE int Sets the receive filter packet type
IPX_STOPFILTERPTYPE int Stops filtering the filter type set with IPX_FILTERTYPE
IPX_DSTYPE int Sets the value of the data stream field in the SPX header on every packet sent.
IPX_EXTENDED_ADDRESS BOOL Sets whether extended addressing is enabled.
IPX_RECVHDR BOOL Sets whether the protocol header is sent up on all receive headers.
IPX_RECEIVE_BROADCAST BOOL Indicates broadcast packets are likely on the socket. Set to TRUE by default. Applications that do not use broadcasts should set this to FALSE for better system performance.
IPX_IMMEDIATESPXACK BOOL Directs SPX connections not to delay before sending an ACK. Applications without back-and-forth traffic should set this to TRUE to increase performance.
SO_ACCEPTCONN BOOL Socket is listening.
SO_RCVLOWAT int Receives low water.
SO_RCVTIMEO int Receives time-out in milliseconds (available in the Microsoft implementation of Windows Sockets 2).
SO_SNDLOWAT int Sends low water.
SO_SNDTIMEO int Sends time-out in milliseconds (available in the Microsoft implementation of Windows Sockets 2).
SO_TYPE int Type of the socket. SO_CONDITIONAL_ACCEPT
Setting this socket option to TRUE delays the acknowledgment of a connection until after the WSAAccept condition function is called. If FALSE, the connection may be accepted before the condition function is called, but the connection will be disconnected if the condition function rejects the call. This option must be set before calling the listen function, otherwise WSAEINVAL is returned. SO_CONDITIONAL_ACCEPT is only supported for TCP and ATM.
TCP sets SO_CONDITIONAL_ACCEPT to FALSE by default, and therefore by default the connection will be accepted before the WSAAccept condition function is called. When set to TRUE, the conditional decision must be made within the TCP connection time-out. CF_DEFER connections are still subject to the time-out.ATM sets SO_CONDITIONAL_ACCEPT to TRUE by default.SO_DEBUG
Windows Sockets service providers are encouraged (but not required) to supply output debug information if the SO_DEBUG option is set by an application. The mechanism for generating the debug information and the form it takes are beyond the scope of this document.
SO_GROUP_PRIORITY
Reserved for future use with socket groups. Group priority indicates the relative priority of the specified socket relative to other sockets within the socket group. Values are nonnegative integers, with zero corresponding to the highest priority. Priority values represent a hint to the underlying service provider about how potentially scarce resources should be allocated. For example, whenever two or more sockets are both ready to transmit data, the highest priority socket (lowest value for SO_GROUP_PRIORITY) should be serviced first with the remainder serviced in turn according to their relative priorities.
SO_KEEPALIVE
An application can request that a TCP/IP provider enable the use of keep-alive packets on TCP connections by turning on the SO_KEEPALIVE socket option. A Windows Sockets provider need not support the use of keep-alives. If it does, the precise semantics are implementation-specific but should conform to section 4.2.3.6 of RFC 1122: Requirements for Internet Hosts—Communication Layers. If a connection is dropped as the result of keep-alives the error code WSAENETRESET is returned to any calls in progress on the socket, and any subsequent calls will fail with WSAENOTCONN.
SO_LINGER
The SO_LINGER option controls the action taken when unsent data is queued on a socket and a closesocket is performed. See closesocket for a description of the way in which the SO_LINGER settings affect the semantics of closesocket. The application sets the desired behavior by creating a LINGER structure (pointed to by the optval parameter) with these members l_onoff and l_linger set appropriately.
SO_REUSEADDR
By default, a socket cannot be bound (see bind) to a local address that is already in use. On occasion, however, it can be necessary to reuse an address in this way. Since every connection is uniquely identified by the combination of local and remote addresses, there is no problem with having two sockets bound to the same local address as long as the remote addresses are different. To inform the Windows Sockets provider that a bind on a socket should not be disallowed because the desired address is already in use by another socket, the application should set the SO_REUSEADDR socket option for the socket before issuing the bind. The option is interpreted only at the time of the bind. It is therefore unnecessary and harmless to set the option on a socket that is not to be bound to an existing address. Setting or resetting the option after the bind has no effect on this or any other socket.
SO_RCVBUF and SO_SNDBUF
When a Windows Sockets implementation supports the SO_RCVBUF and SO_SNDBUF options, an application can request different buffer sizes (larger or smaller). The call to setsockopt can succeed even when the implementation did not provide the whole amount requested. An application must call getsockopt with the same option to check the buffer size actually provided.
SO_RCVTIMEO and SO_SNDTIMEO
When using the recv function, if no data arrives during the period specified in SO_RCVTIMEO, the recv function completes. In Windows versions prior to Windows 2000, any data received subsequently fails with WSAETIMEDOUT. In Windows 2000 and later, if no data arrives within the period specified in SO_RCVTIMEO the recv function returns WSAETIMEDOUT, and if data is received, recv returns SUCCESS.
If a send or receive operation times out on a socket, the socket state is indeterminate, and should not be used; TCP sockets in this state have a potential for data loss, since the operation could be canceled at the same moment the operation was to be completed.PVD_CONFIG
This object stores the configuration information for the service provider associated with the socket specified in the s parameter. The exact format of this data structure is specific to each service provider.
TCP_NODELAY
The TCP_NODELAY option is specific to TCP/IP service providers. The Nagle algorithm is disabled if the TCP_NODELAY option is enabled (and vice versa). The process involves buffering send data when there is unacknowledged data already in flight or buffering send data until a full-size packet can be sent. It is highly recommended that TCP/IP service providers enable the Nagle Algorithm by default, and for the vast majority of application protocols the Nagle Algorithm can deliver significant performance enhancements. However, for some applications this algorithm can impede performance, and TCP_NODELAY can be used to turn it off. These are applications where many small messages are sent, and the time delays between the messages are maintained. Application writers should not set TCP_NODELAY unless the impact of doing so is well-understood and desired because setting TCP_NODELAY can have a significant negative impact on network and application performance.
Example Code
The following example demonstrates the setsockopt function.#include <stdio.h>
#include "winsock2.h"void main() { //---------------------------------------
// Declare variables
WSADATA wsaData;
SOCKET ListenSocket;
sockaddr_in service; //---------------------------------------
// Initialize Winsock
int iResult = WSAStartup( MAKEWORD(2,2), &wsaData );
if( iResult != NO_ERROR )
printf("Error at WSAStartup\n"); //---------------------------------------
// Create a listening socket
ListenSocket = socket( AF_INET, SOCK_STREAM, IPPROTO_TCP );
if (ListenSocket == INVALID_SOCKET) {
printf("Error at socket()\n");
WSACleanup();
return;
} //---------------------------------------
// Bind the socket to the local IP address
// and port 27015
hostent* thisHost;
char* ip;
u_short port;
port = 27015;
thisHost = gethostbyname("");
ip = inet_ntoa (*(struct in_addr *)*thisHost->h_addr_list); service.sin_family = AF_INET;
service.sin_addr.s_addr = inet_addr(ip);
service.sin_port = htons(port); if ( bind( ListenSocket,(SOCKADDR*) &service, sizeof(service) ) == SOCKET_ERROR ) {
printf("bind failed\n");
closesocket(ListenSocket);
return;
} //---------------------------------------
// Initialize variables and call setsockopt.
// The SO_KEEPALIVE parameter is a socket option
// that makes the socket send keepalive messages
// on the session. The SO_KEEPALIVE socket option
// requires a boolean value to be passed to the
// setsockopt function. If TRUE, the socket is
// configured to send keepalive messages, if FALSE
// the socket configured to NOT send keepalive messages.
// This section of code tests the setsockopt function
// by checking the status of SO_KEEPALIVE on the socket
// using the getsockopt function.
BOOL bOptVal = TRUE;
int bOptLen = sizeof(BOOL);
int iOptVal;
int iOptLen = sizeof(int); if (getsockopt(ListenSocket, SOL_SOCKET, SO_KEEPALIVE, (char*)&iOptVal, &iOptLen) != SOCKET_ERROR) {
printf("SO_KEEPALIVE Value: %ld\n", iOptVal);
} if (setsockopt(ListenSocket, SOL_SOCKET, SO_KEEPALIVE, (char*)&bOptVal, bOptLen) != SOCKET_ERROR) {
printf("Set SO_KEEPALIVE: ON\n");
} if (getsockopt(ListenSocket, SOL_SOCKET, SO_KEEPALIVE, (char*)&iOptVal, &iOptLen) != SOCKET_ERROR) {
printf("SO_KEEPALIVE Value: %ld\n", iOptVal);
} WSACleanup();
return;}
Notes for IrDA SocketsKeep in mind the following:
The Af_irda.h header file must be explicitly included.
IrDA provides the following settable socket option:
Value Type Meaning
IRLMP_IAS_SET *IAS_SET Sets IAS attributes
The IRLMP_IAS_SET socket option enables the application to set a single attribute of a single class in the local IAS. The application specifies the class to set, the attribute, and attribute type. The application is expected to allocate a buffer of the necessary size for the passed parameters.IrDA provides an IAS database that stores IrDA-based information. Limited access to the IAS database is available through the Windows Sockets 2 interface, but such access is not normally used by applications, and exists primarily to support connections to non-Windows devices that are not compliant with the Windows Sockets 2 IrDA conventions.The following structure, IAS_SET, is used with the IRLMP_IAS_SET setsockopt option to manage the local IAS database:
typedef struct _IAS_SET {
char irdaClassName[IAS_MAX_CLASSNAME];
char irdaAttribName[IAS_MAX_ATTRIBNAME];
u_long irdaAttribType;
union
{
LONG irdaAttribInt;
struct
{
u_short Len;
u_char OctetSeq[IAS_MAX_OCTET_STRING];
} irdaAttribOctetSeq;
struct
{
u_char Len;
u_char CharSet;
u_char UsrStr[IAS_MAX_USER_STRING];
} irdaAttribUsrStr;
} irdaAttribute;
} IAS_SET, *PIAS_SET, FAR *LPIAS_SET;The following structure, IAS_QUERY, is used with the IRLMP_IAS_QUERY setsockopt option to query a peer's IAS database:
typedef struct _WINDOWS_IAS_QUERY {
u_char irdaDeviceID[4];
char irdaClassName[IAS_MAX_CLASSNAME];
char irdaAttribName[IAS_MAX_ATTRIBNAME];
u_long irdaAttribType;
union
{
LONG irdaAttribInt;
struct
{
u_long Len;
u_char OctetSeq[IAS_MAX_OCTET_STRING];
} irdaAttribOctetSeq;
struct
{
u_long Len;
u_long CharSet;
u_char UsrStr[IAS_MAX_USER_STRING];
} irdaAttribUsrStr;
} irdaAttribute;
} IAS_QUERY, *PIAS_QUERY, FAR *LPIAS_QUERY;Many SO_ level socket options are not meaningful to IrDA. Only SO_LINGER is specifically supported.Note setsockopt must be called before bind on Windows NT 4.0, Windows 95, and Windows 98 platforms.
Requirements
Client Requires Windows XP, Windows 2000 Professional, Windows NT Workstation, Windows Me, Windows 98, or Windows 95.
Server Requires Windows Server 2003, Windows 2000 Server, or Windows NT Server.
Header Declared in Winsock2.h.
Library Link to Ws2_32.lib.
DLL Requires Ws2_32.dll. See Also
setsockopt( m_Socket, SOL_SOCKET, SO_DONTLINGER, (char *)&sopt, sizeof(BOOL));u_long nonBlock = FALSE;
ioctlsocket(m_Socket, FIONBIO, &nonBlock);