getaddrinfo(3)						     Linux Programmer's Manual						    getaddrinfo(3)

NAME

       getaddrinfo - network address and service translation

SYNOPSIS

       #include <sys/types.h>
       #include <sys/socket.h>
       #include <netdb.h>

       int getaddrinfo(const char *node, const char *service,
		       const struct addrinfo *hints,
		       struct addrinfo **res);

       void freeaddrinfo(struct addrinfo *res);

       const char *gai_strerror(int errcode);

DESCRIPTION

       The  getaddrinfo(3)  function combines the functionality provided by the getipnodebyname(3), getipnodebyaddr(3), getservbyname(3), and get-
       servbyport(3) functions into a single interface.  The thread-safe getaddrinfo(3) function creates one or  more  socket  address	structures
       that can be used by the bind(2) and connect(2) system calls to create a client or a server socket.

       The  getaddrinfo(3)  function  is  not limited to creating IPv4 socket address structures; IPv6 socket address structures can be created if
       IPv6 support is available.  These socket address structures can be used directly by bind(2) or connect(2), to prepare a client or a  server
       socket.

       The addrinfo structure used by this function contains the following members:

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

       getaddrinfo(3) sets res to point to a dynamically-allocated link list of addrinfo structures, linked by the ai_next member.  There are sev-
       eral reasons why the link list may have more than one addrinfo structure, including: if the network host is multi-homed;  or  if  the  same
       service is available from multiple socket protocols (one SOCK_STREAM address and another SOCK_DGRAM address, for example).

       The  members  ai_family,  ai_socktype,  and ai_protocol have the same meaning as the corresponding parameters in the socket(2) system call.
       The getaddrinfo(3) function returns socket addresses in either IPv4 or IPv6 address family, (ai_family will be set  to  either  PF_INET	or
       PF_INET6).

       The  hints  parameter  specifies  the  preferred  socket type, or protocol.  A NULL hints specifies that any network address or protocol is
       acceptable.  If this parameter is not NULL it points to an addrinfo structure whose ai_family, ai_socktype, and ai_protocol members specify
       the  preferred  socket type.  PF_UNSPEC in ai_family specifies any protocol family (either IPv4 or IPv6, for example).  0 in ai_socktype or
       ai_protocol specifies that any socket type or protocol is acceptable as well.  The ai_flags member specifies  additional  options,  defined
       below.	Multiple  flags are specified by logically OR-ing them together.  All the other members in the hints parameter must contain either
       0, or a null pointer.

       The node or service parameter, but not both, may be NULL.  node specifies either a numerical network  address  (dotted-decimal  format  for
       IPv4,  hexadecimal  format  for IPv6) or a network hostname, whose network addresses are looked up and resolved.  If the ai_flags member in
       the hints parameter contains the AI_NUMERICHOST flag then the node parameter must be a numerical network address.  The AI_NUMERICHOST  flag
       suppresses any potentially lengthy network host address lookups.

       The getaddrinfo(3) function creates a link list of addrinfo structures, one for each network address subject to any restrictions imposed by
       the hints parameter.  ai_canonname is set to point to the official name of the host, if ai_flags in hints includes the  AI_CANONNAME  flag.
       ai_family,  ai_socktype,  and ai_protocol specify the socket creation parameters.  A pointer to the socket address is placed in the ai_addr
       member, and the length of the socket address, in bytes, is placed in the ai_addrlen member.

       If node is NULL, the network address in each socket structure is initialized according to the AI_PASSIVE flag, which is set in the ai_flags
       member  of  the hints parameter.  The network address in each socket structure will be left unspecified if AI_PASSIVE flag is set.  This is
       used by server applications, which intend to accept client connections on any network address.  The network address  will  be  set  to  the
       loopback  interface  address  if  the AI_PASSIVE flag is not set.  This is used by client applications, which intend to connect to a server
       running on the same network host.

       service sets the port number in the network address of each socket structure.  If service is NULL the port number will be  left	uninitial-
       ized.

       The freeaddrinfo(3) function frees the memory that was allocated for the dynamically allocated link list res.

RETURN VALUE

       getaddrinfo(3) returns 0 if it succeeds, or one of the following non-zero error codes:

       EAI_FAMILY
	      The requested address family is not supported at all.

       EAI_SOCKTYPE
	      The requested socket type is not supported at all.

       EAI_BADFLAGS
	      ai_flags contains invalid flags.

       EAI_NONAME
	      The node or service is not known.  This error is also returned if both node and service are NULL.

       EAI_SERVICE
	      The requested service is not available for the requested socket type.  It may be available through another socket type.

       EAI_ADDRFAMILY
	      The specified network host does not have any network addresses in the requested address family.

       EAI_NODATA
	      The specified network host exists, but does not have any network addresses defined.

       EAI_MEMORY
	      Out of memory.

       EAI_FAIL
	      The name server returned a permanent failure indication.

       EAI_AGAIN
	      The name server returned a temporary failure indication.	Try again later.

       EAI_SYSTEM
	      Other system error, check errno for details.

       The gai_strerror(3) function translates these error codes to a human readable string, suitable for error reporting.

SEE ALSO

       getipnodebyname(3), getipnodebyaddr(3)

Linux Man Page							    2000-12-18							    getaddrinfo(3)