Address Information Structure

The <netdb.h> header shall define the addrinfo structure that includes 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 macros 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 macros that evaluate to bitwise-distinct integer constants for use in the flags argument to getnameinfo(3):

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_DGRAM

Indicates that the service is a datagram service (SOCK_DGRAM).

Address Information Errors

The <netdb.h> header shall define the following macros for use as error values for getaddrinfo(3) and getnameinfo(3):

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   *gethostbyaddr(const void *, socklen_t, int);
struct hostent   *gethostbyname(const char *);
struct hostent   *gethostent(void);
int               getnameinfo(const struct sockaddr *restrict, socklen_t,
                      char *restrict, socklen_t, char *restrict,
                      socklen_t, unsigned);
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 type socklen_t shall be defined 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.