netdb.h(0P)		   POSIX Programmer's Manual		   netdb.h(0P)

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 .

IEEE/The Open Group		     2017			   netdb.h(0P)