V10/man/man3/internet.3

.TH INTERNET 3X
.CT 2 comm_mach
.SH NAME
in_host, in_ntoa, in_address, in_service \- internet networking functions
.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 long port;
.fi
.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
.SM ASCII
representation of an
.I in_addr
can be either a host name or of the form
.I b1.b2.b3.b4,
where each
.I `bx'
is the value of the
.IR x 'th
byte of the
address in decimal.
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
and returns 0
if the name is not found in the host
table.
.PP
.I In_host
maps an internet address into a host name.
If the host is not found in the host table, the
.SM ASCII
representation of the address is returned.
.PP
.I In_ntoa
maps an internet address to its
.SM ASCII
numeric format.
.PP
.I In_service
returns the closest match to
.I name
in the services file.
If either
.I name
or
.I port
are 0,
they will match any name or port.
If
.I proto
is
.BR "(char *)0" ,
the
.B tcp
protocol is assumed.
.SH FILES
.nf
.ta 32n
\fL/usr/inet/lib/hosts\fP	mapping between host names and addresses
\fL/usr/inet/lib/networks\fP	mapping between network names and addresses
\fL/usr/inet/lib/services\fP	database of services
\fL/usr/inet/lib/hosts.equiv\fP	machines with common administration
.fi
.SH SEE ALSO
.IR ipc (3),
.IR tcp (3), 
.IR 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.