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GETNAMEINFO(3P)            POSIX Programmer's Manual           GETNAMEINFO(3P)
PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       getnameinfo -- get name information
SYNOPSIS
       #include <sys/socket.h>
       #include <netdb.h>
       int getnameinfo(const struct sockaddr *restrict sa, socklen_t salen,
           char *restrict node, socklen_t nodelen, char *restrict service,
           socklen_t servicelen, int flags);
DESCRIPTION
       The getnameinfo() function shall translate a socket address to  a  node
       name  and  service  location,  all  of  which are defined as in freead-
       drinfo().
       The sa argument points to a socket address structure to be  translated.
       The salen argument contains the length of the address pointed to by sa.
       If the socket address structure contains an IPv4-mapped IPv6 address or
       an IPv4-compatible IPv6 address, the implementation shall  extract  the
       embedded IPv4 address and lookup the node name for that IPv4 address.
       If  the  address is the IPv6 unspecified address ("::"), a lookup shall
       not be performed and the behavior shall be the same as when the  node's
       name cannot be located.
       If  the node argument is non-NULL and the nodelen argument is non-zero,
       then the node argument points to a buffer able to contain up to nodelen
       bytes  that  receives the node name as a null-terminated string. If the
       node argument is NULL or the nodelen argument is zero,  the  node  name
       shall  not  be  returned.  If  the  node's  name cannot be located, the
       numeric form of the address contained in the socket  address  structure
       pointed to by the sa argument is returned instead of its name.
       If the service argument is non-NULL and the servicelen argument is non-
       zero, then the service argument points to a buffer able to  contain  up
       to servicelen bytes that receives the service name as a null-terminated
       string.  If the service argument is NULL or the servicelen argument  is
       zero,  the  service  name  shall not be returned. If the service's name
       cannot be located, the numeric form of the service address  (for  exam-
       ple, its port number) shall be returned instead of its name.
       The  flags  argument  is a flag that changes the default actions of the
       function. By default the fully-qualified domain  name  (FQDN)  for  the
       host shall be returned, but:
        *  If the flag bit NI_NOFQDN is set, only the node name portion of the
           FQDN shall be returned for local hosts.
        *  If the flag bit NI_NUMERICHOST is set,  the  numeric  form  of  the
           address contained in the socket address structure pointed to by the
           sa argument shall be returned instead of its name.
        *  If the flag bit NI_NAMEREQD is set, an error shall be  returned  if
           the host's name cannot be located.
        *  If the flag bit NI_NUMERICSERV is set, the numeric form of the ser-
           vice address shall be  returned  (for  example,  its  port  number)
           instead of its name.
        *  If  the  flag  bit  NI_NUMERICSCOPE is set, the numeric form of the
           scope identifier shall be returned (for example,  interface  index)
           instead  of its name. This flag shall be ignored if the sa argument
           is not an IPv6 address.
        *  If the flag bit NI_DGRAM is set, this indicates that the service is
           a  datagram service (SOCK_DGRAM). The default behavior shall assume
           that the service is a stream service (SOCK_STREAM).
       Notes:
                  1. The two NI_NUMERICxxx flags are required to  support  the
                     -n flag that many commands provide.
                  2. The  NI_DGRAM  flag  is  required for the few AF_INET and
                     AF_INET6 port numbers (for example, [512,514]) that  rep-
                     resent different services for UDP and TCP.
       The getnameinfo() function shall be thread-safe.
RETURN VALUE
       A  zero return value for getnameinfo() indicates successful completion;
       a non-zero return value indicates failure. The possible values for  the
       failures are listed in the ERRORS section.
       Upon  successful  completion,  getnameinfo()  shall return the node and
       service names, if requested, in  the  buffers  provided.  The  returned
       names are always null-terminated strings.
ERRORS
       The  getnameinfo()  function  shall  fail  and return the corresponding
       value if:
       [EAI_AGAIN] The name  could  not  be  resolved  at  this  time.  Future
                   attempts may succeed.
       [EAI_BADFLAGS]
                   The flags had an invalid value.
       [EAI_FAIL]  A non-recoverable error occurred.
       [EAI_FAMILY]
                   The address family was not recognized or the address length
                   was invalid for the specified family.
       [EAI_MEMORY]
                   There was a memory allocation failure.
       [EAI_NONAME]
                   The name does not resolve for the supplied parameters.
                   NI_NAMEREQD is set and the host's name cannot  be  located,
                   or both nodename and servname were null.
       [EAI_OVERFLOW]
                   An argument buffer overflowed. The buffer pointed to by the
                   node argument or the service argument was too small.
       [EAI_SYSTEM]
                   A system error occurred. The error code  can  be  found  in
                   errno.
       The following sections are informative.
EXAMPLES
       None.
APPLICATION USAGE
       If the returned values are to be used as part of any further name reso-
       lution (for example, passed to getaddrinfo()), applications should pro-
       vide buffers large enough to store any result possible on the system.
       Given the IPv4-mapped IPv6 address "::ffff:1.2.3.4", the implementation
       performs a lookup as if the socket address structure contains the  IPv4
       address "1.2.3.4".
       The  IPv6  unspecified  address  ("::")  and  the IPv6 loopback address
       ("::1") are not IPv4-compatible addresses.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       endservent(), freeaddrinfo(), gai_strerror(), inet_ntop(), socket()
       The Base Definitions volume of POSIX.1-2008, <netdb.h>, <sys_socket.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained  online
       at http://www.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                      GETNAMEINFO(3P)