netdb.h (0p) - Linux Man Pages

netdb.h: definitions for network database operations

NAME

netdb.h - definitions for network database operations

SYNOPSIS

#include <netdb.h>

DESCRIPTION

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.

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.

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>.

The following sections are informative.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

SEE ALSO

<netinet/in.h>, <inttypes.h>, <sys/socket.h>, the System Interfaces volume of IEEE Std 1003.1-2001, bind(), endhostent(), endnetent(), endprotoent(), endservent(), getaddrinfo(), getnameinfo()