NAME

netdb - definitions for network database operations

SYNOPSIS

#include <netdb.h>

DESCRIPTION

The <netdb.h> header defines the type in_port_t and the type in_addr_t as described in in(5).

The <netdb.h> header defines the hostent structure that includes the following members:

char   * h_name         Official name of the net.
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 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.
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   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 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 for h_errno:

        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

Inclusion of the <netdb.h> header may also make visible all symbols from in(5).

Default

For applications that do not require standard-conforming behavior (those that use the socket interfaces described in section 3N of the reference manual; see Intro(3) and standards(5)), the following are declared as functions, and may also be defined as macros:

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

Standard-conforming

For applications that require standard-conforming behavior (those that use the socket interfaces described in section 3XN of the reference manual; see Intro(3) and standards(5)), 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(constvoid * addr, size_t len, int type);
struct hostent    * gethostbyname(constchar * name);
struct hostent    * gethostent(void);
struct netent     * getnetbyaddr(in_addr_tnet, int type);
struct netent     * getnetbyname(constchar * name);
struct netent     * getnetent(void);
struct protoent   * getprotobyname(constchar * name);
struct protoent   * getprotobynumber(intproto);
struct protoent   * getprotoent(void);
struct servent    * getservbyname(constchar * name, const char * proto);
struct servent    * getservbyport(intport, const char * proto);
struct servent    * getservent(void);

void              sethostent(int stayopen);
void              setnetent(int stayopen);
void              setprotoent(int stayopen);
void              setservent(int stayopen);

SEE ALSO

Intro(3), endhostent(3N), endhostent(3XN), endnetent(3N), endnetent(3XN), endprotoent(3N), endprotoent(3XN), endservent(3N), endservent(3XN), in(5), standards(5)