netdb.h(3)                 POSIX Programmer's Manual                netdb.h(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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(3)
