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.
