getnameinfo - Get a node name and service name for an
address and port number
#include <netdb.h>
int getnameinfo(
const struct sockaddr *sa,
socklen_t salen,
char *node,
size_t *nodelen,
char *serv,
size_t servlen,
int flags );
Standard C Library (libc)
Points either to a sockaddr_in structure (for IPv4) or to
a sockaddr_in6 structure (for IPv6) that holds the IP
address and port number. Specifies the length of either
the sockaddr_in structure or the sockaddr_in6 structure.
Points to a buffer in which to receive the null-terminated
network node name or address (either global address or
scoped address withh scope identifier) contained in sa. A
NULL pointer instructs the routine not to return a node
name. Both node and serv cannot be zero. Specifies the
length of the node buffer. A value of zero instructs the
routine not to return a node name. Points to a buffer in
which to receive the null-terminated network service name
associated with the port number contained in sa. A NULL
pointer instructs the routine not to return a service
name. Both node and serv cannot be zero. Specifies the
length of the serv buffer. A value of zero instructs the
routine not to return a service name. Specifies changes
to the routine's default actions. By default, the routine
searches for the fully-qualified domain name of the node
in the hosts database and returns it. See the "Flag Bits"
section for additional flags.
The getnameinfo() routine looks up an IP address and port
number in a sockaddr structure specified by sa and returns
node name and service name text strings in the buffers
pointed to by the node and serv parameters, respectively.
If the node's name is not found, the routine returns the
numeric form of the node's address, regardless of the
value of the flags parameter. If the service's name is
not found, the routine returns the numeric form of the
service's address (port number) regardless of the value of
the flags parameter.
The application must provide buffers large enough to hold
the fully-qualified domain name and the service name,
including the terminating null characters. To assist in
initializing the buffers, the following constants are
defined in <netdb.h>:
#define NI_MAXHOST 1025 #define NI_MAXSERV 32
Flag Bits [Toc] [Back]
The flag bits and their meanings, if set, are as follows:
Specifies that the service is a datagram service
(SOCK_DGRAM). The default is to assume a stream service
(SOCK_STREAM). This is required for the few ports
(512-514) that have different services for UDP and TCP.
Returns an error if the host's name cannot be located in
the hosts database. Searches the hosts database and
returns the node name portion of the fully-qualified
domain name for local hosts. Returns the numeric form of
the host's address instead of its name. No host name resolution
is performed. Returns the interface index instead
of the interface name for scoped addresses. The address is
returned in scoped address format. No host name resolution
is performed.
[Tru64 UNIX] For scoped addresses, either of the
following formats is used:
link-local-address%interface-id link-localaddress%interface-name
Returns the numeric form
(port number) of the service address instead of its
name. No service name resolution is performed.
The two NI_NUMERIC* flags are required to support the -n
option that many commands provide. All flags are defined
in <netdb.h> header file.
Upon successful completion, the getnameinfo() function
returns 0 (zero). Upon failure, it returns a non-zero
value.
If the getnameinfo() function fails, it returns one of the
following values: The nodename parameter could not be
resolved this time. Try the request again. The value of
the flags parameter is invalid. A non-recoverable error
occurred. The address family (ai_family in the hints
structure) was not recognized, or the address length was
invalid. A memory allocation failure occurred. Name does
not resolve to supplied parameters.
The NI_NAMEREQD flag was set and the node's name
was not found.
You did not pass either the nodename or servname
parameter. You must pass at least one. A system
error occurred; errno is set to the error value.
The Internet network hostname database. Each record in
the file occupies a single line and has three fields consisting
of the host address, official hostname, and
aliases. The resolver configuration file. The database
service selection configuration file.
Functions: gai_strerror(3), getaddrinfo(3), getservbyname(3), gethostbyport(3), inet_ntop(3), socket(3).
Files: hostname(5), resolv.conf(4), svc.conf(4).
Networks: bind_intro(7), nis_intro(7).
Network Programmer's Guide
getnameinfo(3)
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