GetAddrInfoW function (ws2tcpip.h)

Article
08/23/2022

The GetAddrInfoW function provides protocol-independent translation from a Unicode host name to an address.

Syntax

INT WSAAPI GetAddrInfoW(
  [in, optional] PCWSTR          pNodeName,
  [in, optional] PCWSTR          pServiceName,
  [in, optional] const ADDRINFOW *pHints,
  [out]          PADDRINFOW      *ppResult
);

Parameters

[in, optional] pNodeName

A pointer to a NULL-terminated Unicode string that contains a host (node) name or a numeric host address string. For the Internet protocol, the numeric host address string is a dotted-decimal IPv4 address or an IPv6 hex address.

[in, optional] pServiceName

A pointer to a NULL-terminated Unicode string that contains either a service name or port number represented as a string.

A service name is a string alias for a port number. For example, “http” is an alias for port 80 defined by the Internet Engineering Task Force (IETF) as the default port used by web servers for the HTTP protocol. Possible values for the pServiceName parameter when a port number is not specified are listed in the following file:

%WINDIR%\system32\drivers\etc\services

[in, optional] pHints

A pointer to an addrinfoW structure that provides hints about the type of socket the caller supports.

The ai_addrlen, ai_canonname, ai_addr, and ai_next members of the addrinfoW structure pointed to by the pHints parameter must be zero or NULL. Otherwise the GetAddrInfoEx function will fail with WSANO_RECOVERY.

See the Remarks for more details.

[out] ppResult

A pointer to a linked list of one or more addrinfoW structures that contains response information about the host.

Return value

Success returns zero. Failure returns a nonzero Windows Sockets error code, as found in the Windows Sockets Error Codes.

Most nonzero error codes returned by the GetAddrInfoW function map to the set of errors outlined by Internet Engineering Task Force (IETF) recommendations. The following table lists these error codes and their WSA equivalents. It is recommended that the WSA error codes be used, as they offer familiar and comprehensive error information for Winsock programmers.

Error value	WSA equivalent	Description
EAI_AGAIN	WSATRY_AGAIN	A temporary failure in name resolution occurred.
EAI_BADFLAGS	WSAEINVAL	An invalid value was provided for the ai_flags member of the pHints parameter.
EAI_FAIL	WSANO_RECOVERY	A nonrecoverable failure in name resolution occurred.
EAI_FAMILY	WSAEAFNOSUPPORT	The ai_family member of the pHints parameter is not supported.
EAI_MEMORY	WSA_NOT_ENOUGH_MEMORY	A memory allocation failure occurred.
EAI_NONAME	WSAHOST_NOT_FOUND	The name does not resolve for the supplied parameters or the pNodeName and pServiceName parameters were not provided.
EAI_SERVICE	WSATYPE_NOT_FOUND	The pServiceName parameter is not supported for the specified ai_socktype member of the pHints parameter.
EAI_SOCKTYPE	WSAESOCKTNOSUPPORT	The ai_socktype member of the pHints parameter is not supported.

Use the gai_strerror function to print error messages based on the EAI_* codes returned by the GetAddrInfoW function. The gai_strerror function is provided for compliance with IETF recommendations, but it is not thread safe. Therefore, use of a traditional Windows Sockets function, such as WSAGetLastError, is recommended.

Error code	Meaning
WSA_NOT_ENOUGH_MEMORY	There was insufficient memory to perform the operation.
WSAEAFNOSUPPORT	An address incompatible with the requested protocol was used. This error is returned if the ai_family member of the addrinfoW structure pointed to by the hints parameter is not supported.
WSAEINVAL	An invalid argument was supplied. This error is returned if an invalid value was provided for the ai_flags member of the addrinfoW structure pointed to by the hints parameter.
WSAESOCKTNOSUPPORT	The support for the specified socket type does not exist in this address family. This error is returned if the ai_socktype member of the addrinfoW structure pointed to by the hints parameter is not supported.
WSAHOST_NOT_FOUND	No such host is known. This error is returned if the name does not resolve for the supplied parameters or the pNodename and pServicename parameters were not provided.
WSANO_DATA	The requested name is valid, but no data of the requested type was found.
WSANO_RECOVERY	A nonrecoverable error occurred during a database lookup. This error is returned if nonrecoverable error in name resolution occurred.
WSANOTINITIALISED	A successful WSAStartup call must occur before using this function.
WSATRY_AGAIN	This is usually a temporary error during hostname resolution and means that the local server did not receive a response from an authoritative server. This error is returned when a temporary failure in name resolution occurred.
WSATYPE_NOT_FOUND	The specified class was not found. The pServiceName parameter is not supported for the specified ai_socktype member of the addrinfoW structure pointed to by the hints parameter.

Remarks

The GetAddrInfoW function is the Unicode version of a function that provides protocol-independent translation from host name to address. The ANSI version of this function is getaddrinfo.

The GetAddrInfoW function returns results for the NS_DNS namespace. The GetAddrInfoW function aggregates all responses if more than one namespace provider returns information. For use with the IPv6 and IPv4 protocol, name resolution can be by the Domain Name System (DNS), a local hosts file, or by other naming mechanisms for the NS_DNS namespace.

Macros in the Winsock header file define a mixed-case function name of GetAddrInfo and a ADDRINFOT structure. This GetAddrInfo function should be called with the pNodeName and pServiceName parameters of a pointer of type TCHAR and the pHints and ppResult parameters of a pointer of type ADDRINFOT. When UNICODE or _UNICODE is defined, GetAddrInfo is defined to GetAddrInfoW, the Unicode version of the function, and ADDRINFOT is defined to the addrinfoW structure. When UNICODE or _UNICODE is not defined, GetAddrInfo is defined to getaddrinfo, the ANSI version of the function, and ADDRINFOT is defined to the addrinfo structure.

One or both of the pNodeName or pServiceName parameters must point to a NULL-terminated Unicode string; generally both are provided.

Upon success, a linked list of addrinfoW structures is returned in the ppResult parameter. The list can be processed by following the pointer provided in the ai_next member of each returned addrinfoW structure until a NULL pointer is encountered. In each returned addrinfoW 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 addrinfoW structure points to a filled-in socket address structure, the length of which is specified in its ai_addrlen member.

If the pNodeName parameter points to a computer name, all permanent addresses for the computer that can be used as a source address are returned. On Windows Vista and later, these addresses would include all unicast IP addresses returned by the GetUnicastIpAddressTable or GetUnicastIpAddressEntry functions in which the SkipAsSource member is set to false in the MIB_UNICASTIPADDRESS_ROW structure.

If the pNodeName parameter points to a string equal to "localhost", all loopback addresses on the local computer are returned.

If the pNodeName parameter contains an empty string, all registered addresses on the local computer are returned.

On Windows Server 2003 and later if the pNodeName parameter points to a string equal to "..localmachine", all registered addresses on the local computer are returned.

If the pNodeName parameter refers to a cluster virtual server name, only virtual server addresses are returned. On Windows Vista and later, these addresses would include all unicast IP addresses returned by the GetUnicastIpAddressTable or GetUnicastIpAddressEntry functions in which the SkipAsSource member is set to true in the MIB_UNICASTIPADDRESS_ROW structure. See Windows Clustering for more information about clustering.

Windows 7 with Service Pack 1 (SP1) and Windows Server 2008 R2 with Service Pack 1 (SP1) add support to Netsh.exe for setting the SkipAsSource attribute on an IP address. This also changes the behavior such that if the SkipAsSource member in the MIB_UNICASTIPADDRESS_ROW structure is set to false, the IP address will be registered in DNS. If the SkipAsSource member is set to true, the IP address is not registered in DNS.

A hotfix is available for Windows 7 and Windows Server 2008 R2 that adds support to Netsh.exe for setting the SkipAsSource attribute on an IP address. This hotfix also changes behavior such that if the SkipAsSource member in the MIB_UNICASTIPADDRESS_ROW structure is set to false, the IP address will be registered in DNS. If the SkipAsSource member is set to true, the IP address is not registered in DNS. For more information, see Knowledge Base (KB) 2386184.

A similar hotfix is also available for Windows Vista with Service Pack 2 (SP2) and Windows Server 2008 with Service Pack 2 (SP2) that adds support to Netsh.exe for setting the SkipAsSource attribute on an IP address. This hotfix also changes behavior such that if the SkipAsSource member in the MIB_UNICASTIPADDRESS_ROW structure is set to false, the IP address will be registered in DNS. If the SkipAsSource member is set to true, the IP address is not registered in DNS.

Callers of the GetAddrInfoW function can provide hints about the type of socket supported through an addrinfoW structure pointed to by the pHints parameter. When the pHints parameter is used, the following rules apply to its associated addrinfoW structure:

A value of AF_UNSPEC for ai_family indicates the caller will accept only the AF_INET and AF_INET6 address families. Note that AF_UNSPEC and PF_UNSPEC are the same.
A value of zero for ai_socktype indicates the caller will accept any socket type.
A value of zero for ai_protocol indicates the caller will accept any protocol.
The ai_addrlen member must be set to zero.
The ai_canonname member must be set to NULL.
The ai_addr member must be set to NULL.
The ai_next member must be set to NULL.

Other values in the addrinfoW structure provided in the pHints parameter indicate specific requirements. For example, if the caller handles only IPv4 and does not handle IPv6, the ai_family member should be set to AF_INET. For another example, if the caller handles only TCP and does not handle UDP, the ai_socktype member should be set to SOCK_STREAM.

If the pHints parameter is a NULL pointer, the GetAddrInfoW function handles it as if the addrinfoW structure in pHints were initialized with its ai_family member set to AF_UNSPEC and all other members set to zero.

On Windows Vista and later when GetAddrInfoW is called from a service, if the operation is the result of a user process calling the service, then the service should impersonate the user. This is to allow security to be properly enforced.

The GetAddrInfoW function can be used to convert a text string representation of an IP address to an addrinfoW structure that contains a sockaddr structure for the IP address and other information. To be used in this way, the string pointed to by the pNodeName parameter must contain a text representation of an IP address and the addrinfoW structure pointed to by the pHints parameter must have the AI_NUMERICHOST flag set in the ai_flags member. The string pointed to by the pNodeName parameter may contain a text representation of either an IPv4 or an IPv6 address. The text IP address is converted to an addrinfoW structure pointed to by the ppResult parameter. The returned addrinfoW structure contains a sockaddr structure for the IP address along with additional information about the IP address. For this method to work with an IPv6 address string on Windows Server 2003 and Windows XP, the IPv6 protocol must be installed on the local computer. Otherwise, the WSAHOST_NOT_FOUND error is returned.

Freeing Address Information from Dynamic Allocation

All information returned by the GetAddrInfoW function pointed to by the ppResult parameter is dynamically allocated, including all addrinfoW structures, socket address structures, and canonical host name strings pointed to by addrinfoW structures. Memory allocated by a successful call to this function must be released with a subsequent call to FreeAddrInfoW.

Example Code

The following code example shows how to use the GetAddrInfoW function.

#ifndef UNICODE
#define UNICODE
#endif

#define WIN32_LEAN_AND_MEAN

#include <winsock2.h>
#include <Ws2tcpip.h>
#include <stdio.h>

// Link with ws2_32.lib
#pragma comment(lib, "Ws2_32.lib")

// set APPVER=5.02 for WinXP SP2 and later

int __cdecl wmain(int argc, wchar_t **argv)
{

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

    DWORD dwRetval;

    int i = 1;
    
    ADDRINFOW *result = NULL;
    ADDRINFOW *ptr = NULL;
    ADDRINFOW hints;

//    struct sockaddr_in6 *sockaddr_ipv6;
    LPSOCKADDR sockaddr_ip;

    wchar_t ipstringbuffer[46];
    DWORD ipbufferlength = 46;

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


    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        wprintf(L"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;

    wprintf(L"Calling getaddrinfow with following parameters:\n");
    wprintf(L"\tnodename = %ws\n", argv[1]);
    wprintf(L"\tservname (or port) = %ws\n\n", argv[2]);
    

//--------------------------------
// Call GetAddrinfoW(). If the call succeeds,
// the result variable will hold a linked list
// of addrinfow structures containing response
// information
    dwRetval = GetAddrInfoW(argv[1], argv[2], &hints, &result);
    if ( dwRetval != 0 ) {
        wprintf(L"GetAddrInfoW failed with error: %d\n", dwRetval);
        WSACleanup();
        return 1;
    }

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

        wprintf(L"GetAddrInfoW response %d\n", i++);
        wprintf(L"\tFlags: 0x%x\n", ptr->ai_flags);
        wprintf(L"\tFamily: ");
        switch (ptr->ai_family) {
            case AF_UNSPEC:
                wprintf(L"Unspecified\n");
                break;
            case AF_INET:
                wprintf(L"AF_INET (IPv4)\n");
                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)
                    wprintf(L"WSAAddressToString failed with %u\n", WSAGetLastError() );
                else    
                    wprintf(L"\tIPv4 address %ws\n", ipstringbuffer);
                break;
            case AF_INET6:
                wprintf(L"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)
                    wprintf(L"WSAAddressToString failed with %u\n", WSAGetLastError() );
                else    
                    wprintf(L"\tIPv6 address %ws\n", ipstringbuffer);
                break;
            default:
                wprintf(L"Other %ld\n", ptr->ai_family);
                break;
        }
        wprintf(L"\tSocket type: ");
        switch (ptr->ai_socktype) {
            case 0:
                wprintf(L"Unspecified\n");
                break;
            case SOCK_STREAM:
                wprintf(L"SOCK_STREAM (stream)\n");
                break;
            case SOCK_DGRAM:
                wprintf(L"SOCK_DGRAM (datagram) \n");
                break;
            case SOCK_RAW:
                wprintf(L"SOCK_RAW (raw) \n");
                break;
            case SOCK_RDM:
                wprintf(L"SOCK_RDM (reliable message datagram)\n");
                break;
            case SOCK_SEQPACKET:
                wprintf(L"SOCK_SEQPACKET (pseudo-stream packet)\n");
                break;
            default:
                wprintf(L"Other %ld\n", ptr->ai_socktype);
                break;
        }
        wprintf(L"\tProtocol: ");
        switch (ptr->ai_protocol) {
            case 0:
                wprintf(L"Unspecified\n");
                break;
            case IPPROTO_TCP:
                wprintf(L"IPPROTO_TCP (TCP)\n");
                break;
            case IPPROTO_UDP:
                wprintf(L"IPPROTO_UDP (UDP) \n");
                break;
            default:
                wprintf(L"Other %ld\n", ptr->ai_protocol);
                break;
        }
        wprintf(L"\tLength of this sockaddr: %d\n", ptr->ai_addrlen);
        wprintf(L"\tCanonical name: %s\n", ptr->ai_canonname);
    }

    FreeAddrInfoW(result);
    WSACleanup();

    return 0;
}

Note Ensure that the development environment targets the newest version of Ws2tcpip.h which includes structure and function definitions for addrinfoW and GetAddrInfoW, respectively.

Internationalized Domain Names

Internet host names typically consist of a very restricted set of characters:

Upper and lower case ASCII letters from the English alphabet.
Digits from 0 to 9.
ASCII hyphen characters.

With the growth of the Internet, there is a growing need to identify Internet host names for other languages not represented by the ASCII character set. Identifiers which facilitate this need and allow non-ASCII characters (Unicode) to be represented as special ASCII character strings are known as Internationalized Domain Names (IDNs). A mechanism called Internationalizing Domain Names in Applications (IDNA) is used to handle IDNs in a standard fashion. The specifications for IDNs and IDNA are documented in RFC 3490, RTF 5890, and RFC 6365 published by the Internet Engineering Task Force (IETF).

On Windows 8 and Windows Server 2012, the GetAddrInfoW function provides support for Internationalized Domain Name (IDN) parsing applied to the name passed in the pNodeName parameter. Winsock performs Punycode/IDN encoding and conversion. This behavior can be disabled using the AI_DISABLE_IDN_ENCODING flag discussed below.

On Windows 7 and Windows Server 2008 R2 or earlier, the GetAddrInfoW function does not currently provide support for IDN parsing applied to the name passed in the pNodeName parameter. Winsock does not perform any Punycode/IDN conversion. The GetAddrInfoW function does not use Punycode to convert an IDN as per RFC 3490. The GetAddrInfoW function when querying DNS encodes the Unicode name in UTF-8 format, the format used by Microsoft DNS servers in an enterprise environment.

Several functions on Windows Vista and later support conversion between Unicode labels in an IDN to their ASCII equivalents. The resulting representation of each Unicode label contains only ASCII characters and starts with the xn-- prefix if the Unicode label contained any non-ASCII characters. The reason for this is to support existing DNS servers on the Internet, since some DNS tools and servers only support ASCII characters (see RFC 3490).

The IdnToAscii function use Punycode to convert an IDN to the ASCII representation of the original Unicode string using the standard algorithm defined in RFC 3490. The IdnToUnicode function converts the ASCII form of an IDN to the normal Unicode UTF-16 encoding syntax. For more information and links to related draft standards, see Handling Internationalized Domain Names (IDNs).

The IdnToAscii function can be used to convert an IDN name to the ASCII form. To pass this ASCII form to the GetAddrInfoW function, you can use the MultiByteToWideChar function to convert the CHAR string into a WCHAR string that then can be passed in the pNodeName parameter to the GetAddrInfoW function.

Use of ai_flags in the hints parameter

Flags in the ai_flags member of the optional addrinfoW structure provided in the pHints parameter modify the behavior of the function.

These flag bits are defined in the Ws2def.h header file on the Microsoft Windows Software Development Kit (SDK) for Windows 7. These flag bits are defined in the Ws2tcpip.h header file on the Windows SDK for Windows Server 2008 and Windows Vista. These flag bits are defined in the Ws2tcpip.h header file on the Platform Software Development Kit (SDK) for Windows Server 2003, and Windows XP.

The flag bits can be a combination of the following:

Flag Bits	Description
AI_PASSIVE	Setting the AI_PASSIVE flag indicates the caller intends to use the returned socket address structure in a call to the bind function. When the AI_PASSIVE flag is set and pNodeName is a NULL pointer, the IP address portion of the socket address structure is set to INADDR_ANY for IPv4 addresses and IN6ADDR_ANY_INIT for IPv6 addresses. When the AI_PASSIVE flag is not set, the returned socket address structure is ready for a call to the connect function for a connection-oriented protocol, or ready for a call to either the connect, sendto, or send functions for a connectionless protocol. If the pNodeName parameter is a NULL pointer in this case, the IP address portion of the socket address structure is set to the loopback address.
AI_CANONNAME	If neither AI_CANONNAME nor AI_NUMERICHOST is used, the GetAddrInfoW function attempts resolution. If a literal string is passed GetAddrInfoW attempts to convert the string, and if a host name is passed the GetAddrInfoW function attempts to resolve the name to an address or multiple addresses. When the AI_CANONNAME bit is set, the pNodeName parameter cannot be NULL. Otherwise the GetAddrInfoEx function will fail with WSANO_RECOVERY. When the AI_CANONNAME bit is set and the GetAddrInfoW function returns success, the ai_canonname member in the ppResult parameter points to a NULL-terminated string that contains the canonical name of the specified node. Note The GetAddrInfoW function can return success when the AI_CANONNAME flag is set, yet the ai_canonname member in the associated addrinfoW structure is NULL. Therefore, the recommended use of the AI_CANONNAME flag includes testing whether the ai_canonname member in the associated addrinfoW structure is NULL.
AI_NUMERICHOST	When the AI_NUMERICHOST bit is set, the pNodeName parameter must contain a non-NULL numeric host address string, otherwise the EAI_NONAME error is returned. This flag prevents a name resolution service from being called.
AI_NUMERICSERV	When the AI_NUMERICSERV bit is set, the pServiceName parameter must contain a non-NULL numeric port number, otherwise the EAI_NONAME error is returned. This flag prevents a name resolution service from being called. The AI_NUMERICSERV flag is defined on Windows SDK for Windows Vista and later. The AI_NUMERICSERV flag is not supported by Microsoft providers.
AI_ALL	If the AI_ALL bit is set, a request is made for IPv6 addresses and IPv4 addresses with AI_V4MAPPED. The AI_ALL flag is defined on the Windows SDK for Windows Vista and later. The AI_ALL flag is supported on Windows Vista and later.
AI_ADDRCONFIG	If the AI_ADDRCONFIG bit is set, GetAddrInfoW will resolve only if a global address is configured. If AI_ADDRCONFIG flag is specified, IPv4 addresses shall be returned only if an IPv4 address is configured on the local system, and IPv6 addresses shall be returned only if an IPv6 address is configured on the local system. The IPv4 or IPv6 loopback address is not considered a valid global address. The AI_ADDRCONFIG flag is defined on the Windows SDK for Windows Vista and later. The AI_ADDRCONFIG flag is supported on Windows Vista and later.
AI_V4MAPPED	If the AI_V4MAPPED bit is set and a 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. The AI_V4MAPPED flag is defined on the Windows SDK for Windows Vista and later. The AI_V4MAPPED flag is supported on Windows Vista and later.
AI_NON_AUTHORITATIVE	If the AI_NON_AUTHORITATIVE bit is set, the NS_EMAIL namespace provider returns both authoritative and non-authoritative results. If the AI_NON_AUTHORITATIVE bit is not set, the NS_EMAIL namespace provider returns only authoritative results. The AI_NON_AUTHORITATIVE flag is defined on the Windows SDK for Windows Vista and later. The AI_NON_AUTHORITATIVE flag is supported on Windows Vista and later and applies only to the NS_EMAIL namespace.
AI_SECURE	If the AI_SECURE bit is set, the NS_EMAIL namespace provider will return results that were obtained with enhanced security to minimize possible spoofing. The AI_SECURE flag is defined on the Windows SDK for Windows Vista and later. The AI_SECURE flag is supported on Windows Vista and later and applies only to the NS_EMAIL namespace.
AI_RETURN_PREFERRED_NAMES	If the AI_RETURN_PREFERRED_NAMES is set, then no name should be provided in the pNodeName parameter. The NS_EMAIL namespace provider will return preferred names for publication. The AI_RETURN_PREFERRED_NAMES flag is defined on the Windows SDK for Windows Vista and later. The AI_RETURN_PREFERRED_NAMES flag is supported on Windows Vista and later and applies only to the NS_EMAIL namespace.
AI_FQDN	If the AI_FQDN is set and a flat name (single label) is specified, GetAddrInfoW 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 in the associated addrinfoW structure. 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 GetAddrInfoW function will fail if both flags are present with EAI_BADFLAGS. When the AI_FQDN bit is set, the pNodeName parameter cannot be NULL. Otherwise the GetAddrInfoEx function will fail with WSANO_RECOVERY. Windows 7: The AI_FQDN flag is defined on the Windows SDK for Windows 7 and later. The AI_FQDN flag is supported on Windows 7 and later.
AI_FILESERVER	If the AI_FILESERVER is set, this is a hint to the namespace provider that the hostname being queried is being used in file share scenario. The namespace provider may ignore this hint. Windows 7: The AI_FILESERVER flag is defined on the Windows SDK for Windows 7 and later. The AI_FILESERVER flag is supported on Windows 7 and later.
AI_DISABLE_IDN_ENCODING	If the AI_DISABLE_IDN_ENCODING is set, this disables the automatic International Domain Name encoding using Punycode in the name resolution functions called by the GetAddrInfoW function. Windows 8: The AI_DISABLE_IDN_ENCODING flag is defined on the Windows SDK for Windows 8 and later. The AI_DISABLE_IDN_ENCODING flag is supported on Windows 8 and later.

Windows 8.1 and Windows Server 2012 R2: This function is supported for Windows Store apps on Windows 8.1, Windows Server 2012 R2, and later.

Note

The ws2tcpip.h header defines GetAddrInfo as an alias which automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.

Requirements

Requirement	Value
Minimum supported client	Windows 8.1, Windows Vista [desktop apps \| UWP apps]
Minimum supported server	Windows Server 2003 [desktop apps \| UWP apps]
Target Platform	Windows
Header	ws2tcpip.h
Library	Ws2_32.lib
DLL	Ws2_32.dll