V8/usr/man/man3/internet.3

.TH INTERNET 3 
.SH NAME
in_host, in_ntoa, in_address, in_service - internet operations
.SH SYNOPSIS
.nf
.B #include <sys/inet/in.h>
.PP
.B char *in_host(hostaddr)
.B in_addr hostaddr;
.PP
.B char *in_ntoa(hostaddr)
.B in_addr hostaddr;
.PP
.B in_addr in_address(hostname)
.B char *hostname;
.PP
.B struct in_service *in_service(name, proto, port)
.B char *name, *proto;
.B unsigned int port;
.PP
.SH DESCRIPTION
These routines are loaded by the 
.B \-lin
option of
.IR ld (1).
.PP
Internet addresses, type
.I in_addr,
are 32 bit quantities global to the network.
The ascii representation for an
.I in_addr
can be either a host name or the form
.I b1.b2.b3.b4,
where each 
.I `bx'
is the value of the x'th byte of the
address in decimal.
The mapping of an internet address to a host name is an
.I n
to
.I m
mapping.
Since host names are considered local `aliases' for internet
addresses, the host to address mapping is subjective.
.PP
.I In_address
maps an internet host name to an address.
.PP
.I In_host
maps an internet address into a host name.
.PP
.I In_ntoa
maps an internet address to its ascii numeric format.
.PP
.I In_service
looks up an entry in the services file and returns the
closest match.
If either
.I name
or 
.I port
are 0, they will match any name or port.
If 
.I proto
is 0, the ``tcp'' protocol is assumed.
.SH FILES
.nf
/usr/inet/lib/hosts	mapping between host names and addresses
/usr/inet/lib/networks	mapping between network names and addresses
/usr/inet/lib/services	database of services
/usr/inet/lib/hosts.equiv	machines with common administration
.SH SEE ALSO
tcp(3), udp(3)
.SH BUGS
.PP
The mappings between internet addresses and names is arbitrary at best.
The hosts file may contain many addresses for each name and/or many
names for each address.
.I In_address
and
.I in_host
each start at the beginning of the file and search sequentially for a match.
Therefore, 
.B "in_addr(in_host(addr)) \=\= addr"
is not necessarily true.