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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

       netdb.h — definitions for network database operations

SYNOPSIS

       #include <netdb.h>

DESCRIPTION

       The  <netdb.h> header may define the in_port_t type and the in_addr_t type as described in
       <netinet/in.h>.

       The <netdb.h> header shall define the hostent structure, which shall include at least  the
       following members:

           char   *h_name       Official name of the host.
           char  **h_aliases    A pointer to an array of pointers to
                                alternative host names, terminated by a
                                null pointer.
           int     h_addrtype   Address type.
           int     h_length     The length, in bytes, of the address.
           char  **h_addr_list  A pointer to an array of pointers to network
                                addresses (in network byte order) for the host,
                                terminated by a null pointer.

       The  <netdb.h>  header shall define the netent structure, which shall include at least the
       following members:

           char     *n_name      Official, fully-qualified (including the
                                 domain) name of the host.
           char    **n_aliases   A pointer to an array of pointers to
                                 alternative network names, terminated by a
                                 null pointer.
           int       n_addrtype  The address type of the network.
           uint32_t  n_net       The network number, in host byte order.

       The <netdb.h> header shall define the uint32_t type as described in <inttypes.h>.

       The <netdb.h> header shall define the protoent structure, which shall include at least the
       following members:

           char   *p_name     Official name of the protocol.
           char  **p_aliases  A pointer to an array of pointers to
                              alternative protocol names, terminated by
                              a null pointer.
           int     p_proto    The protocol number.

       The  <netdb.h> header shall define the servent structure, which shall include at least the
       following members:

           char   *s_name     Official name of the service.
           char  **s_aliases  A pointer to an array of pointers to
                              alternative service names, terminated by
                              a null pointer.
           int     s_port     A value which, when converted to uint16_t,
                              yields the port number in network byte order
                              at which the service resides.
           char   *s_proto    The name of the protocol to use when
                              contacting the service.

       The <netdb.h> header shall define the IPPORT_RESERVED symbolic constant with the value  of
       the highest reserved Internet port number.

   Address Information Structure
       The <netdb.h> header shall define the addrinfo structure, which shall include at least the
       following members:

           int               ai_flags      Input flags.
           int               ai_family     Address family of socket.
           int               ai_socktype   Socket type.
           int               ai_protocol   Protocol of socket.
           socklen_t         ai_addrlen    Length of socket address.
           struct sockaddr  *ai_addr       Socket address of socket.
           char             *ai_canonname  Canonical name of service location.
           struct addrinfo  *ai_next       Pointer to next in list.

       The <netdb.h> header shall define  the  following  symbolic  constants  that  evaluate  to
       bitwise-distinct integer constants for use in the flags field of the addrinfo structure:

       AI_PASSIVE    Socket address is intended for bind().

       AI_CANONNAME  Request for canonical name.

       AI_NUMERICHOST
                     Return numeric host address as name.

       AI_NUMERICSERV
                     Inhibit service name resolution.

       AI_V4MAPPED   If  no IPv6 addresses are found, query for IPv4 addresses and return them to
                     the caller as IPv4-mapped IPv6 addresses.

       AI_ALL        Query for both IPv4 and IPv6 addresses.

       AI_ADDRCONFIG Query for IPv4 addresses only when an IPv4 address is configured; query  for
                     IPv6 addresses only when an IPv6 address is configured.

       The  <netdb.h>  header  shall  define  the  following  symbolic constants that evaluate to
       bitwise-distinct integer constants for use in the flags argument to getnameinfo():

       NI_NOFQDN     Only the nodename portion of the FQDN is returned for local hosts.

       NI_NUMERICHOST
                     The numeric form of the node's address is returned instead of its name.

       NI_NAMEREQD   Return an error if the node's name cannot be located in the database.

       NI_NUMERICSERV
                     The numeric form of the service address is returned instead of its name.

       NI_NUMERICSCOPE
                     For IPv6 addresses, the numeric form of the  scope  identifier  is  returned
                     instead of its name.

       NI_DGRAM      Indicates that the service is a datagram service (SOCK_DGRAM).

   Address Information Errors
       The <netdb.h> header shall define the following symbolic constants for use as error values
       for getaddrinfo() and getnameinfo().   The  values  shall  be  suitable  for  use  in  #if
       preprocessing directives.

       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_SERVICE   The service passed was not recognized for the specified socket type.

       EAI_SOCKTYPE  The intended socket type was not recognized.

       EAI_SYSTEM    A system error occurred. The error code can be found in errno.

       EAI_OVERFLOW  An argument buffer overflowed.

       The  following  shall be declared as functions and may also be defined as macros. Function
       prototypes shall be provided.

           void              endhostent(void);
           void              endnetent(void);
           void              endprotoent(void);
           void              endservent(void);
           void              freeaddrinfo(struct addrinfo *);
           const char       *gai_strerror(int);
           int               getaddrinfo(const char *restrict, const char *restrict,
                                 const struct addrinfo *restrict,
                                 struct addrinfo **restrict);
           struct hostent   *gethostent(void);
           int               getnameinfo(const struct sockaddr *restrict, socklen_t,
                                 char *restrict, socklen_t, char *restrict,
                                 socklen_t, int);
           struct netent    *getnetbyaddr(uint32_t, int);
           struct netent    *getnetbyname(const char *);
           struct netent    *getnetent(void);
           struct protoent  *getprotobyname(const char *);
           struct protoent  *getprotobynumber(int);
           struct protoent  *getprotoent(void);
           struct servent   *getservbyname(const char *, const char *);
           struct servent   *getservbyport(int, const char *);
           struct servent   *getservent(void);
           void              sethostent(int);
           void              setnetent(int);
           void              setprotoent(int);
           void              setservent(int);

       The <netdb.h> header shall define the socklen_t type  through  typedef,  as  described  in
       <sys/socket.h>.

       Inclusion  of  the <netdb.h> header may also make visible all symbols from <netinet/in.h>,
       <sys/socket.h>, and <inttypes.h>.

       The following sections are informative.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       <inttypes.h>, <netinet_in.h>, <sys_socket.h>

       The  System  Interfaces  volume  of  POSIX.1‐2017,  bind(),   endhostent(),   endnetent(),
       endprotoent(), endservent(), freeaddrinfo(), gai_strerror(), getnameinfo()

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1-2017, Standard for Information Technology -- Portable  Operating  System  Interface
       (POSIX),  The  Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by
       the Institute of Electrical and Electronics Engineers, Inc and The  Open  Group.   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.opengroup.org/unix/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 .