netdb.h(7POSIX)

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 .