gai_strerror
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 struc-
ture, 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 mean-
ing 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 accept-
able. If this parameter is not NULL it points to an addrinfo structure
whose ai_family, ai_socktype, and ai_protocol members specify the pre-
ferred socket type. PF_UNSPEC in ai_family specifies any protocol fam-
ily (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 speci-
fies 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 parame-
ter must be a numerical network address. The AI_NUMERICHOST flag sup-
presses 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_fam-
ily, ai_socktype, and ai_protocol specify the socket creation parame-
ters. 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 ini-
tialized 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 loop-
back 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)
