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.TH ARES_INIT 3 "7 December 2004"
ares_init, ares_init_options \- Initialize a resolver channel
.B #include <ares.h>
.B int ares_init(ares_channel *\fIchannel\fP)
.B int ares_init_options(ares_channel *\fIchannel\fP,
.B struct ares_options *\fIoptions\fP, int \fIoptmask\fP)
.B cc file.c -lcares
The \fBares_init\fP function initializes a communications channel for name
service lookups. If it returns successfully, \fBares_init\fP will set the
variable pointed to by \fIchannel\fP to a handle used to identify the name
service channel. The caller should invoke
.BR ares_destroy (3)
on the handle when the channel is no longer needed.
The \fBares_init_options\fP function also initializes a name service channel,
with additional options useful for applications requiring more control over
name service configuration. The \fIoptmask\fP parameter specifies which fields
in the structure pointed to by \fIoptions\fP are set, as follows:
.TP 18
.B int \fIflags\fP;
Flags controlling the behavior of the resolver. See below for a
description of possible flag values.
.TP 18
.B int \fItimeout\fP;
The number of seconds each name server is given to respond to a query
on the first try. (After the first try, the timeout algorithm becomes
more complicated, but scales linearly with the value of
\fItimeout\fP.) The default is five seconds.
.TP 18
.B int \fItries\fP;
The number of tries the resolver will try contacting each name server
before giving up. The default is four tries.
.TP 18
.B int \fIndots\fP;
The number of dots which must be present in a domain name for it to be
queried for "as is" prior to querying for it with the default domain
extensions appended. The default value is 1 unless set otherwise by
resolv.conf or the RES_OPTIONS environment variable.
.TP 18
.B unsigned short \fIport\fP;
The port to use for queries (both TCP and UDP), in network byte order.
The default value is 53 (in network byte order), the standard name
service port.
.TP 18
.B struct in_addr *\fIservers\fP;
.B int \fInservers\fP;
The list of servers to contact, instead of the servers specified in
resolv.conf or the local named.
.TP 18
.B char **\fIdomains\fP;
.B int \fIndomains\fP;
The domains to search, instead of the domains specified in resolv.conf
or the domain derived from the kernel hostname variable.
.TP 18
.B char *\fIlookups\fP;
The lookups to perform for host queries.
.I lookups
should be set to a string of the characters "b" or "f", where "b"
indicates a DNS lookup and "f" indicates a lookup in the hosts file.
.I flags
field should be the bitwise or of some subset of the following values:
.TP 23
Always use TCP queries (the "virtual circuit") instead of UDP
queries. Normally, TCP is only used if a UDP query yields a truncated
.TP 23
Only query the first server in the list of servers to query.
.TP 23
If a truncated response to a UDP query is received, do not fall back
to TCP; simply continue on with the truncated response.
.TP 23
Do not set the "recursion desired" bit on outgoing queries, so that the name
server being contacted will not try to fetch the answer from other servers if
it doesn't know the answer locally. Be aware that ares will not do the
recursion for you. Recursion must be handled by the application calling ares
.TP 23
Do not close communciations sockets when the number of active queries
drops to zero.
.TP 23
Do not use the default search domains; only query hostnames as-is or
as aliases.
.TP 23
Do not honor the HOSTALIASES environment variable, which normally
specifies a file of hostname translations.
.TP 23
Do not discard responses with the SERVFAIL, NOTIMP, or REFUSED
response code or responses whose questions don't match the questions
in the request. Primarily useful for writing clients which might be
used to test or debug name servers.
.I ares_init
.I ares_init_options
can return any of the following values:
.TP 14
Initialization succeeded.
.TP 14
A configuration file could not be read.
.TP 14
The process's available memory was exhausted.
.BR ares_destroy (3)
Greg Hudson, MIT Information Systems
Copyright 1998 by the Massachusetts Institute of Technology.