Address Database

Network Address Database Functionality More...

Topics
	addrinfo ai_flags
	Flags for ai_flags in struct addrinfo
	getaddrinfo() Error Values
	Errors for the getaddrinfo() function
	h_errno Error Values
	Error values for the h_errno variable

Files
file	netdb.h
	Network address database functionality.

Data Structures
struct	hostent
	Network host entry. More...
struct	addrinfo
	Network address information structure. More...

Functions
void	freeaddrinfo (struct addrinfo *ai)
	Free an address information structure returned by getaddrinfo().
int	getaddrinfo (const char *nodename, const char *servname, const struct addrinfo *hints, struct addrinfo **res)
	Get information about a specified address.
struct hostent *	gethostbyname (const char *name)
	Look up a host by its name.
struct hostent *	gethostbyname2 (const char *name, int af)
	Look up a host by its name and address family.

Variables
int	h_errno
	Error value for gethostbyname().

Detailed Description

Network Address Database Functionality

Function Documentation

freeaddrinfo()

void freeaddrinfo

(

struct addrinfo *

ai

)

Free an address information structure returned by getaddrinfo().

This function cleans up any memory associated with the specified struct addrinfo, which was returned previously by a call to getaddrinfo().

Parameters

ai	The struct addrinfo to clean up.

getaddrinfo()

int getaddrinfo	(	const char *	nodename,
		const char *	servname,
		const struct addrinfo *	hints,
		struct addrinfo **	res )

Get information about a specified address.

This function translates the name of a host and service into a set of socket addresses and related information to be used in creating a socket. This includes potentially looking up the host information in the network address database (and thus in DNS possibly as well).

Parameters

nodename	The host to look up.
servname	The service to look up.
hints	Hints used in aiding lookup.
res	The resulting address information.

Returns

0 on success, non-zero error code on failure.

See also

getaddrinfo() Error Values

gethostbyname()

struct hostent * gethostbyname

(

const char *

name

)

Look up a host by its name.

This function queries the network address database (possibly recursively) for the network address of the specified hostname. This will first search any local databases before querying remote databases (such as a DNS server) for the host specified.

Parameters

name	The hostname to look up.

Returns

A pointer to a host entry on success or NULL on failure. h_errno is set on failure to indicate the error that occurred.

Note

This function is non-reentrant. getaddrinfo() should (in general) be used instead of this function.

gethostbyname2()

struct hostent * gethostbyname2	(	const char *	name,
		int	af )

Look up a host by its name and address family.

This function queries the network address database (possibly recursively) for the network address of the specified hostname. This will first search any local databases before querying remote databases (such as a DNS server) for the host specified.

This function allows you to specify the address family that you wish the returned hostent to contain. This function is a GNU extension and has not been specified by any POSIX specification.

Parameters

name	The hostname to look up.
af	The address family to use for lookups (AF_INET or AF_INET6).

Returns

A pointer to a host entry on success or NULL on failure. h_errno is set on failure to indicate the error that occurred.

Note

This function is non-reentrant. getaddrinfo() should (in general) be used instead of this function.

Variable Documentation

h_errno

int h_errno

extern

Error value for gethostbyname().

See also

h_errno Error Values