WSAMSG Structure

The WSAMSG structure is used in conjunction with the WSARecvMsg and WSASendMsg functions to store address and optional control information about connected and unconnected sockets as well as an array of buffers used to store message data.

Syntax

typedef struct _WSAMSG {
  LPSOCKADDR name;
  INT        namelen;
  LPWSABUF   lpBuffers;
  DWORD      dwBufferCount;
  WSABUF     Control;
  DWORD      dwFlags;
} WSAMSG, *PWSAMSG, *LPWSAMSG;

Mitglieder

• name
  Typ: LPSOCKADDR

  A pointer to a SOCKET_ADDRESS structure that stores information about the remote address. Used only with unconnected sockets.

• namelen
  Typ: INT

  The length, in bytes, of the SOCKET_ADDRESS structure pointed to in the pAddr member. Used only with unconnected sockets.

• lpBuffers
  Typ: LPWSABUF

  An array of WSABUF structures used to receive the message data. The capability of the lpBuffers member to contain multiple buffers enables the use of scatter/gather I/O.

• dwBufferCount
  Typ: DWORD

  The number of buffers pointed to in the lpBuffers member.

• Control
  Typ: WSABUF

  A structure of WSABUF type used to specify optional control data. See Remarks for more information.

• dwFlags
  Typ: DWORD

  One or more control flags, specified as the logical OR of values. The possible values for dwFlags member on input are defined in the Winsock2.h header file. The possible values for dwFlags member on output are defined in the Ws2def.h header file which is automatically included by the Winsock2.h header file.

  Flags on input	Bedeutung
  MSG_PEEK	Peek at the incoming data. The data is copied into the buffer, but is not removed from the input queue. This flag is valid only for non-overlapped sockets.

   

  Flag returned	Bedeutung
  MSG_BCAST	The datagram was received as a link-layer broadcast or with a destination IP address that is a broadcast address.
  MSG_MCAST	The datagram was received with a destination IP address that is a multicast address.
  MSG_TRUNC	The datagram was truncated. More data was present than the process allocated room for.
  MSG_CTRUNC	The control (ancillary) data was truncated. More control data was present than the process allocated room for.

   

Hinweise

In the Microsoft Windows Software Development Kit (SDK), the version of this structure for use on Windows Vista and defined with the datatype for the dwBufferCount and dwFlags members as a ULONG. When compiling an application if the target platform is Windows Vista and later (NTDDI_VERSION >= NTDDI_LONGHORN, _WIN32_WINNT >= 0x0600, or WINVER >= 0x0600), the datatype for the dwBufferCount and dwFlags members is a ULONG. When compiling an application if the target platform is not Windows Vista and later, the datatype for the dwBufferCount and dwFlags members is a DWORD.

On the Windows SDK released for Windows Vista and later, the organization of header files has changed and the WSAMSG structure is defined in the Ws2def.h header file. Note that the Ws2def.h header file is automatically included in Winsock2.h, and should never be used directly.

If the datagram or control data is truncated during the transmission, the function being used in association with the WSAMSG structure returns SOCKET_ERROR and a call to the WSAGetLastError function returns WSAEMSGSIZE. It is up to the application to determine what was truncated by checking for MSG_TRUNC and/or MSG_CTRUNC flags.

Use of the Control Member

The following table summarizes the various uses of control data available for use in the Control member for IPv4 and IPv6.

Control data is made up of one or more control data objects, each beginning with a WSACMSGHDR structure, defined as the following:

struct wsacmsghdr {
  UINT        cmsg_len;
  INT         cmsg_level;
  INT         cmsg_type;
  /* followed by UCHAR cmsg_data[] */
} WSACMSGHDR;

Hinweis  The transport, not the application, fills out the header information in the WSACMSGHDR structure. The application simply sets the needed socket options and provides the adequate buffer size.

The members of the WSACMSGHDR structure are as follows:

The following macros are used to navigate the data objects:

#define LPCMSGHDR *WSA_CMSG_FIRSTHDR(LPWSAMSG msg);

Returns a pointer to the first control data object. Returns a NULL pointer if there is no control data in the WSAMSG structure, such as when the Control member is a NULL pointer.

#define LPCMSGHDR *WSA_CMSG_NXTHDR(LPWSAMSG msg, LPWSACMSGHDR cmsg);

Returns a pointer to the next control data object, or NULL if there are no more data objects. If the pcmsg parameter is NULL, a pointer to the first control data object is returned.

#define UCHAR *WSA_CMSG_DATA(LPWSACMSGHDR pcmsg);

Returns a pointer to the first byte of data (referred to as the cmsg_data member, though it is not defined in the structure).

#define UINT WSA_CMSG_SPACE(UINT length);

Returns the total size of a control data object, given the amount of data. Used to allocate the correct amount of buffer space. Includes alignment padding.

#define UINT WSA_CMSG_LEN(UINT length);

Returns the value in cmsg_len given the amount of data. Includes alignment padding.

Anforderungen

Siehe auch

IP_PKTINFO

IPV6_PKTINFO

SOCKET_ADDRESS

WSABUF

WSARecv

WSARecvFrom

WSARecvMsg

WSASendMsg