netdb.h, netdb - definitions for network database operations
#include <netdb.h>
The <netdb.h> header defines the type in_port_t and the type in_addr_t as described in in.h(3HEAD).
The <netdb.h> header defines the addrinfo structure, which includes 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 */
See the getaddrinfo(3C) man page for details on the usage of these members in the addrinfo structure.
The <netdb.h> header defines the following symbolic constants that evaluate to bitwise-distinct integer constants for use in the flags field of the addrinfo structure:
Socket address is intended for bind(3C).
Request for canonical name.
Return numeric host address as name.
Inhibit service name resolution.
If no IPv6 addresses are found, query for IPv4 addresses and return them to the caller as IPv4-mapped IPv6 addresses.
Query for both IPv4 and IPv6 addresses.
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 defines the following symbolic constants that evaluate to bitwise-distinct integer constants for use in the flags argument to getnameinfo(3C):
Only the nodename portion of the FQDN is returned for local hosts.
The numeric form of the node's address is returned instead of its name.
Return an error if the node's name cannot be located in the database.
The numeric form of the service address is returned instead of its name.
For IPv6 addresses, the numeric form of the scope identifier is returned instead of its name.
Indicates that the service is a datagram service (SOCK_DGRAM).
The <netdb.h> header defines the following macros for use as error values for getaddrinfo(3C) and getnameinfo(3C). The gai_strerror(3C) function translates these values to error message strings for user presentation.
The name could not be resolved at this time. Future attempts may succeed.
The flags had an invalid value.
A non-recoverable error occurred.
The address family was not recognized or the address length was invalid for the specified family.
There was a memory allocation failure.
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.
The service passed was not recognized for the specified socket type.
The intended socket type was not recognized.
A system error occurred. The error code can be found in errno.
An argument buffer overflowed.
The <netdb.h> header defines the hostent structure that includes the following members:
char *h_name /* official name of the host */
char **h_aliases /* pointer to an array of pointers to
alternative host names, terminated
by a null pointer */
int h_addrtype /* address type */
int h_length /* length, in bytes, of the address */
char **h_addr_list /* 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 defines the netent structure that includes the following members:
char *n_name /* official, fully-qualified */
(including the domain) name
of the network */
char **n_aliases /* pointer to an array of pointers to
alternative network names, terminated */
by a null pointer */
int n_addrtype /* the address type of the network */
in_addr_t n_net /* the network number, in host byte order */
The <netdb.h> header defines the protoent structure that includes the following members:
char *p_name /* official name of the protocol */
char **p_aliases /* pointer to an array of pointers to
alternative protocol names, terminated
by a null pointer */
int p_proto /* protocol number */
The <netdb.h> header defines the servent structure that includes the following members:
char *s_name /* official name of the service */
char **s_aliases /* pointer to an array of pointers to
alternativeservice names, terminated by
a null pointer */
int s_port /* port number at which the service
resides, in network byte order */
char *s_proto /* name of the protocol to use when
contacting the service */
The <netdb.h> header defines the macro IPPORT_RESERVED with the value of the highest normally reserved Internet port number. This will not reflect system configuration changes via the “smallest-nonpriv-port” property which may be set by ipadm(8).
The <netdb.h> header provides a declaration for h_errno:
extern int h_errno;
The <netdb.h> header defines the following macros for use as error values for gethostbyaddr() and gethostbyname():
Inclusion of the <netdb.h> header may also make visible all symbols from in.h(3HEAD) and socket.h(3HEAD).
See attributes(7) for descriptions of the following attributes:
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endhostent(3C), endnetent(3C), endprotoent(3C), endservent(3C), freeaddrinfo(3C), gai_strerror(3C), getaddrinfo(3C), gethostbyname(3C), gethostent(3C), getnameinfo(3C), getnetent(3C), getprotoent(3C), getservbyname(3C), getservent(3C), sethostent(3C), setnetent(3C), setprotoent(3C), setservent(3C), in.h(3HEAD), socket.h(3HEAD), intro(3), attributes(7), standards(7)
Gilligan, R. RFC 3493, Basic Socket Interface Extensions for IPv6. Network Working Group. February 2003. https://tools.ietf.org/html/rfc3493