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 that includes 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 that includes 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 uint32_t type shall be defined as described in <inttypes.h>.
The <netdb.h> header shall define the protoent structure that includes 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 that includes 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 The port number at which the service
resides, in network byte order.
char *s_proto The name of the protocol to use when
contacting the service.
The <netdb.h> header shall define the IPPORT_RESERVED macro with the value of the highest reserved Internet port number.
[OB] ![[Option Start]](../images/opt-start.gif)
When the <netdb.h> header is included, h_errno shall be available as a modifiable lvalue of type int. It
is unspecified whether h_errno is a macro or an identifier declared with external linkage. ![[Option End]](../images/opt-end.gif)
The <netdb.h> header shall define the following macros for use as error values for gethostbyaddr() and gethostbyname():
HOST_NOT_FOUND NO_DATA NO_RECOVERY TRY_AGAIN
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():
- 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 macros for use as error values for getaddrinfo() and getnameinfo():
- 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, 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 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>.