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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 .