PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

GETNAMEINFO(3P)           POSIX Programmer's Manual          GETNAMEINFO(3P)

PROLOG         top

       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         top

       getnameinfo — get name information

SYNOPSIS         top

       #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         top

       The getnameinfo() function shall translate a socket address to a node
       name and service location, all of which are defined as in
       freeaddrinfo(3p).

       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 example, 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
           service 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
                     represent different services for UDP and TCP.

       The getnameinfo() function shall be thread-safe.

RETURN VALUE         top

       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         top

       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         top

       None.

APPLICATION USAGE         top

       If the returned values are to be used as part of any further name
       resolution (for example, passed to getaddrinfo()), applications
       should provide 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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       endservent(3p), freeaddrinfo(3p), gai_strerror(3p), inet_ntop(3p),
       socket(3p)

       The Base Definitions volume of POSIX.1‐2008, netdb.h(0p),
       sys_socket.h(0p)

COPYRIGHT         top

       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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                     GETNAMEINFO(3P)

Pages that refer to this page: netdb.h(0p)freeaddrinfo(3p)