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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  that  includes
       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 that includes 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 uint32_t type shall be defined as described in <inttypes.h> .

       The <netdb.h> header shall define the protoent structure that  includes
       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 that includes
       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     The port number at which the service
                                 resides, in network byte order.
              char   *s_proto    The name of the protocol to use when
                                 contacting the service.

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

       When  the <netdb.h> header is included, h_errno shall be available as a
       modifiable lvalue of type int. It is unspecified whether h_errno  is  a
       macro or an identifier declared with external linkage.

       The <netdb.h> header shall define the following macros for use as error
       values for gethostbyaddr() and gethostbyname():

              HOST_NOT_FOUND
              NO_DATA
              NO_RECOVERY
              TRY_AGAIN

   Address Information Structure
       The <netdb.h> header shall define the addrinfo structure that  includes
       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 macros 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 macros 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 macros for use as error
       values for getaddrinfo() and getnameinfo():

       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   *gethostbyaddr(const void *, socklen_t, int);
              struct hostent   *gethostbyname(const char *);
              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  type  socklen_t  shall  be defined 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

       <netinet/in.h>  , <inttypes.h> , <sys/socket.h> , the System Interfaces
       volume  of  IEEE Std 1003.1-2001,  bind(),  endhostent(),  endnetent(),
       endprotoent(), endservent(), getaddrinfo(), getnameinfo()

COPYRIGHT

       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003  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 .