addrinfo structure

The addrinfo structure is used by the getaddrinfo function to hold host address information.

Syntax


typedef struct addrinfo {
  int             ai_flags;
  int             ai_family;
  int             ai_socktype;
  int             ai_protocol;
  size_t          ai_addrlen;
  char            *ai_canonname;
  struct sockaddr  *ai_addr;
  struct addrinfo  *ai_next;
} ADDRINFOA, *PADDRINFOA;

Members

ai_flags

Type: int

Flags that indicate options used in the getaddrinfo function.

Supported values for the ai_flags member are defined in the Ws2def.h header file on the Windows SDK for Windows 7 and later. These values are defined in the Ws2tcpip.h header file on the Windows SDK for Windows Server 2008 and Windows Vista. These values are defined in the Ws2tcpip.h header file on the Platform SDK for Windows Server 2003, and Windows XP. Supported values for the ai_flags member can be a combination of the following options.

ValueMeaning
AI_PASSIVE
0x01

The socket address will be used in a call to the bind function.

AI_CANONNAME
0x02

The canonical name is returned in the first ai_canonname member.

AI_NUMERICHOST
0x04

The nodename parameter passed to the getaddrinfo function must be a numeric string.

AI_ALL
0x0100

If this bit is set, a request is made for IPv6 addresses and IPv4 addresses with AI_V4MAPPED.

This option is supported on Windows Vista and later.

AI_ADDRCONFIG
0x0400

The getaddrinfo will resolve only if a global address is configured. The IPv6 and IPv4 loopback address is not considered a valid global address.

This option is supported on Windows Vista and later.

AI_V4MAPPED
0x0800

If the getaddrinfo request for IPv6 addresses fails, a name service request is made for IPv4 addresses and these addresses are converted to IPv4-mapped IPv6 address format.

This option is supported on Windows Vista and later.

AI_NON_AUTHORITATIVE
0x04000

The address information can be from a non-authoritative namespace provider.

This option is only supported on Windows Vista and later for the NS_EMAIL namespace.

AI_SECURE
0x08000

The address information is from a secure channel.

This option is only supported on Windows Vista and later for the NS_EMAIL namespace.

AI_RETURN_PREFERRED_NAMES
0x010000

The address information is for a preferred name for a user.

This option is only supported on Windows Vista and later for the NS_EMAIL namespace.

AI_FQDN
0x00020000

If a flat name (single label) is specified, getaddrinfo will return the fully qualified domain name that the name eventually resolved to. The fully qualified domain name is returned in the ai_canonname member.

This is different than AI_CANONNAME bit flag that returns the canonical name registered in DNS which may be different than the fully qualified domain name that the flat name resolved to.

Only one of the AI_FQDN and AI_CANONNAME bits can be set. The getaddrinfo function will fail if both flags are present with EAI_BADFLAGS.

This option is supported on Windows 7, Windows Server 2008 R2, and later.

AI_FILESERVER
0x00040000

A hint to the namespace provider that the hostname being queried is being used in a file share scenario. The namespace provider may ignore this hint.

This option is supported on Windows 7, Windows Server 2008 R2, and later.

 

ai_family

Type: int

The address family. Possible values for the address family are defined in the Winsock2.h header file.

On the Windows SDK released for Windows Vista and later, the organization of header files has changed and the possible values for the address family are 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.

The values currently supported are AF_INET or AF_INET6, which are the Internet address family formats for IPv4 and IPv6. Other options for address family (AF_NETBIOS for use with NetBIOS, for example) are supported if a Windows Sockets service provider for the address family is installed. Note that the values for the AF_ address family and PF_ protocol family constants are identical (for example, AF_UNSPEC and PF_UNSPEC), so either constant can be used.

The following table lists common values for the address family although many other values are possible.

ValueMeaning
AF_UNSPEC
0

The address family is unspecified.

AF_INET
2

The Internet Protocol version 4 (IPv4) address family.

AF_NETBIOS
17

The NetBIOS address family. This address family is only supported if a Windows Sockets provider for NetBIOS is installed.

AF_INET6
23

The Internet Protocol version 6 (IPv6) address family.

AF_IRDA
26

The Infrared Data Association (IrDA) address family. This address family is only supported if the computer has an infrared port and driver installed.

AF_BTH
32

The Bluetooth address family. This address family is only supported if a Bluetooth adapter is installed on Windows Server 2003 or later.

 

ai_socktype

Type: int

The socket type. Possible values for the socket type are defined in the Winsock2.h header file.

The following table lists the possible values for the socket type supported for Windows Sockets 2:

ValueMeaning
SOCK_STREAM
1

Provides sequenced, reliable, two-way, connection-based byte streams with an OOB data transmission mechanism. Uses the Transmission Control Protocol (TCP) for the Internet address family (AF_INET or AF_INET6). If the ai_family member is AF_IRDA, then SOCK_STREAM is the only supported socket type.

SOCK_DGRAM
2

Supports datagrams, which are connectionless, unreliable buffers of a fixed (typically small) maximum length. Uses the User Datagram Protocol (UDP) for the Internet address family (AF_INET or AF_INET6).

SOCK_RAW
3

Provides a raw socket that allows an application to manipulate the next upper-layer protocol header. To manipulate the IPv4 header, the IP_HDRINCL socket option must be set on the socket. To manipulate the IPv6 header, the IPV6_HDRINCL socket option must be set on the socket.

SOCK_RDM
4

Provides a reliable message datagram. An example of this type is the Pragmatic General Multicast (PGM) multicast protocol implementation in Windows, often referred to as reliable multicast programming.

SOCK_SEQPACKET
5

Provides a pseudo-stream packet based on datagrams.

 

In Windows Sockets 2, new socket types were introduced. An application can dynamically discover the attributes of each available transport protocol through the WSAEnumProtocols function. So an application can determine the possible socket type and protocol options for an address family and use this information when specifying this parameter. Socket type definitions in the Winsock2.h and Ws2def.h header files will be periodically updated as new socket types, address families, and protocols are defined.

In Windows Sockets 1.1, the only possible socket types are SOCK_DATAGRAM and SOCK_STREAM.

ai_protocol

Type: int

The protocol type. The possible options are specific to the address family and socket type specified. Possible values for the ai_protocol are defined in the Winsock2.h and Wsrm.h header files.

On the Windows SDK released for Windows Vista and later, the organization of header files has changed and this member can be one of the values from the IPPROTO enumeration type 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 a value of 0 is specified for ai_protocol, the caller does not wish to specify a protocol and the service provider will choose the ai_protocol to use. For protocols other than IPv4 and IPv6, set ai_protocol to zero.

The following table lists common values for the ai_protocol member although many other values are possible.

ValueMeaning
IPPROTO_TCP
6

The Transmission Control Protocol (TCP). This is a possible value when the ai_family member is AF_INET or AF_INET6 and the ai_socktype member is SOCK_STREAM.

IPPROTO_UDP
17

The User Datagram Protocol (UDP). This is a possible value when the ai_family member is AF_INET or AF_INET6 and the type parameter is SOCK_DGRAM.

IPPROTO_RM
113

The PGM protocol for reliable multicast. This is a possible value when the ai_family member is AF_INET and the ai_socktype member is SOCK_RDM. On the Windows SDK released for Windows Vista and later, this value is also called IPPROTO_PGM.

 

If the ai_family member is AF_IRDA, then the ai_protocol must be 0.

ai_addrlen

Type: size_t

The length, in bytes, of the buffer pointed to by the ai_addr member.

ai_canonname

Type: char*

The canonical name for the host.

ai_addr

Type: struct sockaddr*

A pointer to a sockaddr structure. The ai_addr member in each returned addrinfo structure points to a filled-in socket address structure. The length, in bytes, of each returned addrinfo structure is specified in the ai_addrlen member.

ai_next

Type: struct addrinfo*

A pointer to the next structure in a linked list. This parameter is set to NULL in the last addrinfo structure of a linked list.

Remarks

The addrinfo structure is used by the ANSI getaddrinfo function to hold host address information.

The addrinfoW structure is the version of this structure used by the Unicode GetAddrInfoW function.

Macros in the Ws2tcpip.h header file define a ADDRINFOT structure and a mixed-case function name of GetAddrInfo. The GetAddrInfo function should be called with the nodename and servname parameters of a pointer of type TCHAR and the hints and res parameters of a pointer of type ADDRINFOT. When UNICODE or _UNICODE is not defined, ADDRINFOT is defined to the addrinfo structure and GetAddrInfo is defined to getaddrinfo, the ANSI version of this function. When UNICODE or _UNICODE is defined, ADDRINFOT is defined to the addrinfoW structure and GetAddrInfo is defined to GetAddrInfoW, the Unicode version of this function.

Upon a successful call to getaddrinfo, a linked list of addrinfo structures is returned in the res parameter passed to the getaddrinfo function. The list can be processed by following the pointer provided in the ai_next member of each returned addrinfo structure until a NULL pointer is encountered. In each returned addrinfo structure, the ai_family, ai_socktype, and ai_protocol members correspond to respective arguments in a socket or WSASocket function call. Also, the ai_addr member in each returned addrinfo structure points to a filled-in socket address structure, the length of which is specified in its ai_addrlen member.

Support for getaddrinfo and the addrinfo struct on older versions of Windows

The getaddrinfo function that uses the addrinfo structure was added to the Ws2_32.dll on Windows XP and later. The addrinfo structure is defined in the Ws2tcpip.h header file included with the Platform SDK released for Windows XP and later and the Windows SDK released for Windows Vista and later.

To execute an application that uses the getaddrinfo function and the addrinfo structure on earlier versions of Windows (Windows 2000), then you need to include the Ws2tcpip.h and Wspiapi.h files. When the Wspiapi.h include file is added, the getaddrinfo function is defined to the WspiapiGetAddrInfo inline function in the Wspiapi.h file. At runtime, the WspiapiGetAddrInfo function is implemented in such a way that if the Ws2_32.dll or the Wship6.dll (the file containing getaddrinfo in the IPv6 Technology Preview for Windows 2000) does not include getaddrinfo, then a version of getaddrinfo is implemented inline based on code in the Wspiapi.h header file. This inline code will be used on older Windows platforms that do not natively support the getaddrinfo function.

The IPv6 protocol is supported on Windows 2000 when the IPv6 Technology Preview for Windows 2000 is installed. Otherwise getaddrinfo support on versions of Windows earlier than Windows XP is limited to handling IPv4 name resolution.

The GetAddrInfoW function that uses the addrinfoW structure is the Unicode version of the getaddrinfo function and associated addrinfo structure. The GetAddrInfoW function was added to the Ws2_32.dll in Windows XP with Service Pack 2 (SP2). The GetAddrInfoW function and the addrinfoW structure cannot be used on versions of Windows earlier than Windows XP with SP2.

Examples

The following code example shows the use of the addrinfo structure.



#undef UNICODE

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>

// link with Ws2_32.lib
#pragma comment(lib, "Ws2_32.lib")

int __cdecl main(int argc, char **argv)
{

    //-----------------------------------------
    // Declare and initialize variables
    WSADATA wsaData;
    int iResult;
    INT iRetval;

    DWORD dwRetval;

    int i = 1;
    
    struct addrinfo *result = NULL;
    struct addrinfo *ptr = NULL;
    struct addrinfo hints;

    struct sockaddr_in  *sockaddr_ipv4;
//    struct sockaddr_in6 *sockaddr_ipv6;
    LPSOCKADDR sockaddr_ip;

    char ipstringbuffer[46];
    DWORD ipbufferlength = 46;

    // Validate the parameters
    if (argc != 3) {
        printf("usage: %s <hostname> <servicename>\n", argv[0]);
        printf("       provides protocol-independent translation\n");
        printf("       from an ANSI host name to an IP address\n");
        printf("%s example usage\n", argv[0]);
        printf("   %s www.contoso.com 0\n", argv[0]);
        return 1;
    }

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed: %d\n", iResult);
        return 1;
    }

    //--------------------------------
    // Setup the hints address info structure
    // which is passed to the getaddrinfo() function
    ZeroMemory( &hints, sizeof(hints) );
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;

    printf("Calling getaddrinfo with following parameters:\n");
    printf("\tnodename = %s\n", argv[1]);
    printf("\tservname (or port) = %s\n\n", argv[2]);
    
//--------------------------------
// Call getaddrinfo(). If the call succeeds,
// the result variable will hold a linked list
// of addrinfo structures containing response
// information
    dwRetval = getaddrinfo(argv[1], argv[2], &hints, &result);
    if ( dwRetval != 0 ) {
        printf("getaddrinfo failed with error: %d\n", dwRetval);
        WSACleanup();
        return 1;
    }

    printf("getaddrinfo returned success\n");
    
    // Retrieve each address and print out the hex bytes
    for(ptr=result; ptr != NULL ;ptr=ptr->ai_next) {

        printf("getaddrinfo response %d\n", i++);
        printf("\tFlags: 0x%x\n", ptr->ai_flags);
        printf("\tFamily: ");
        switch (ptr->ai_family) {
            case AF_UNSPEC:
                printf("Unspecified\n");
                break;
            case AF_INET:
                printf("AF_INET (IPv4)\n");
                sockaddr_ipv4 = (struct sockaddr_in *) ptr->ai_addr;
                printf("\tIPv4 address %s\n",
                    inet_ntoa(sockaddr_ipv4->sin_addr) );
                break;
            case AF_INET6:
                printf("AF_INET6 (IPv6)\n");
                // the InetNtop function is available on Windows Vista and later
                // sockaddr_ipv6 = (struct sockaddr_in6 *) ptr->ai_addr;
                // printf("\tIPv6 address %s\n",
                //    InetNtop(AF_INET6, &sockaddr_ipv6->sin6_addr, ipstringbuffer, 46) );
                
                // We use WSAAddressToString since it is supported on Windows XP and later
                sockaddr_ip = (LPSOCKADDR) ptr->ai_addr;
                // The buffer length is changed by each call to WSAAddresstoString
                // So we need to set it for each iteration through the loop for safety
                ipbufferlength = 46;
                iRetval = WSAAddressToString(sockaddr_ip, (DWORD) ptr->ai_addrlen, NULL, 
                    ipstringbuffer, &ipbufferlength );
                if (iRetval)
                    printf("WSAAddressToString failed with %u\n", WSAGetLastError() );
                else    
                    printf("\tIPv6 address %s\n", ipstringbuffer);
                break;
            case AF_NETBIOS:
                printf("AF_NETBIOS (NetBIOS)\n");
                break;
            default:
                printf("Other %ld\n", ptr->ai_family);
                break;
        }
        printf("\tSocket type: ");
        switch (ptr->ai_socktype) {
            case 0:
                printf("Unspecified\n");
                break;
            case SOCK_STREAM:
                printf("SOCK_STREAM (stream)\n");
                break;
            case SOCK_DGRAM:
                printf("SOCK_DGRAM (datagram) \n");
                break;
            case SOCK_RAW:
                printf("SOCK_RAW (raw) \n");
                break;
            case SOCK_RDM:
                printf("SOCK_RDM (reliable message datagram)\n");
                break;
            case SOCK_SEQPACKET:
                printf("SOCK_SEQPACKET (pseudo-stream packet)\n");
                break;
            default:
                printf("Other %ld\n", ptr->ai_socktype);
                break;
        }
        printf("\tProtocol: ");
        switch (ptr->ai_protocol) {
            case 0:
                printf("Unspecified\n");
                break;
            case IPPROTO_TCP:
                printf("IPPROTO_TCP (TCP)\n");
                break;
            case IPPROTO_UDP:
                printf("IPPROTO_UDP (UDP) \n");
                break;
            default:
                printf("Other %ld\n", ptr->ai_protocol);
                break;
        }
        printf("\tLength of this sockaddr: %d\n", ptr->ai_addrlen);
        printf("\tCanonical name: %s\n", ptr->ai_canonname);
    }

    freeaddrinfo(result);
    WSACleanup();

    return 0;
}


Requirements

Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]

Header

Ws2tcpip.h;
Wspiapi.h on Windows 2000

See also

addrinfoW
bind
getaddrinfo
GetAddrInfoW
sockaddr
WSAEnumProtocols

 

 

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