<netdb.h>

NAME

netdb.h - definitions for network database operations

SYNOPSIS

#include <netdb.h>

DESCRIPTION

The <netdb.h> header may make available the type in_port_t and the type in_addr_t as defined in the description of <netinet/in.h> .

The <netdb.h> header defines 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 defines 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 uint_32_t type is made available by inclusion of <inttypes.h> (see referenced document XSH).

The <netdb.h> header defines 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 defines 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 defines the macro IPPORT_RESERVED with the value of the highest reserved Internet port number.

The <netdb.h> header provides a declaration of h_errno as a modifiable l-value of type int. For example:

extern int h_errno;

The <netdb.h> header defines the following macros for use as error values for gethostbyaddr() and gethostbyname() :

HOST_NOT_FOUND

NO_DATA

NO_RECOVERY

TRY_AGAIN

The following are declared as functions, and may also be defined as macros:

void endhostent(void);
void endnetent(void);
void endprotoent(void);
void endservent(void);
struct hostent *gethostbyaddr(const void *addr, size_t len, int type);
struct hostent *gethostbyname(const char *name);
struct hostent *gethostent(void);
struct netent *getnetbyaddr(uint32_t net, int type);
struct netent *getnetbyname(const char *name);
struct netent *getnetent(void);
struct protoent *getprotobyname(const char *name);
struct protoent *getprotobynumber(int proto);
struct protoent *getprotoent(void);
struct servent *getservbyname(const char *name, const char *proto);
struct servent *getservbyport(int port, const char *proto);
struct servent *getservent(void);
void sethostent(int stayopen);
void setnetent(int stayopen);
void setprotoent(int stayopen);
void setservent(int stayopen);

Inclusion of the <netdb.h> header may also make visible all symbols from <netinet/in.h> and <inttypes.h> .

SEE ALSO

endhostent() , endnetent() , endprotoent() , endservent() .