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.\" Copyright 1996 Massachusetts Institute of Technology

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.\"     $ANA: addr2ascii.3,v 1.1 1996/06/13 18:41:46 wollman Exp $

.\"     $Id: addr2ascii.3,v 1.2 2001-09-27 12:01:53 chris Exp $

.\"

.Dd June 13, 1996

.Dt ADDR2ASCII 3

.Os

.Sh NAME

.Nm addr2ascii ,

.Nm ascii2addr

.Nd Generic address formatting routines

.Sh SYNOPSIS

.Fd #include 

.Fd #include 

.Fd #include 

.Ft "char *"

.Fn addr2ascii "int af" "const void *addrp" "int len" "char *buf"

.Ft int

.Fn ascii2addr "int af" "const char *ascii" "void *result"

.Sh DESCRIPTION

The routines

.Fn addr2ascii

and

.Fn ascii2addr

are used to convert network addresses between binary form and a

printable form appropriate to the address family.  Both functions take

an

.Fa af

argument, specifying the address family to be used in the conversion

process.

(Currently, only the

.Dv AF_INET

and

.Dv AF_LINK

address families are supported.)

.Pp

The

.Fn addr2ascii

function

is used to convert binary, network-format addresses into printable

form.  In addition to

.Fa af ,

there are three other arguments.  The

.Fa addrp

argument is a pointer to the network address to be converted.

The

.Fa len

argument is the length of the address.  The

.Fa buf

argument is an optional pointer to a caller-allocated buffer to hold

the result; if a null pointer is passed,

.Fn addr2ascii

uses a statically-allocated buffer.

.Pp

The

.Fn ascii2addr

function performs the inverse operation to

.Fn addr2ascii .

In addition to

.Fa af ,

it takes two parameters,

.Fa ascii

and

.Fa result .

The

.Fa ascii

parameter is a pointer to the string which is to be converted into

binary.  The

.Fa result

parameter is a pointer to an appropriate network address structure for

the specified family.

.Pp

The following gives the appropriate structure to use for binary

addresses in the specified family:

.Pp

.Bl -tag -width AF_INETxxxx -compact

.It Dv AF_INET

.Li struct in_addr

.Pq in Aq Pa netinet/in.h

.It Dv AF_LINK

.Li struct sockaddr_dl

.Pq in Aq Pa net/if_dl.h

.\" .It Dv AF_INET6

.\" .Li struct in6_addr

.\" .Pq in Aq Pa netinet6/in6.h

.El

.Sh RETURN VALUES

The

.Fn addr2ascii

function returns the address of the buffer it was passed, or a static

buffer if the a null pointer was passed; on failure, it returns a null

pointer.

The

.Fn ascii2addr

function returns the length of the binary address in bytes, or -1 on

failure.

.Sh EXAMPLES

The

.Xr inet 3

functions

.Fn inet_ntoa

and

.Fn inet_aton

could be implemented thusly:

.Bd -literal -offset indent

#include 

#include 

#include 

#include 

char *

inet_ntoa(struct in_addr addr)

{

        return addr2ascii(AF_INET, &addr, sizeof addr, 0);

}

int

inet_aton(const char *ascii, struct in_addr *addr)

{

        return (ascii2addr(AF_INET, ascii, addr)

            == sizeof(*addr));

}

.Ed

.Pp

In actuality, this cannot be done because

.Fn addr2ascii

and

.Fn ascii2addr

are implemented in terms of the

.Xr inet 3

functions, rather than the other way around.

.Sh ERRORS

When a failure is returned,

.Li errno

is set to one of the following values:

.Bl -tag -width [EPROTONOSUPPORT]

.It Bq Er ENAMETOOLONG

The

.Fn addr2ascii

routine was passed a

.Fa len

parameter which was inappropriate for the address family given by

.Fa af .

.It Bq Er EPROTONOSUPPORT

Either routine was passed an

.Fa af

parameter other than

.Dv AF_INET

or

.Dv AF_LINK .

.It Bq Er EINVAL

The string passed to

.Fn ascii2addr

was improperly formatted for address family

.Fa af .

.El

.Sh SEE ALSO

.Xr inet 3 ,

.Xr linkaddr 3 ,

.Xr inet 4

.Sh HISTORY

An interface close to this one was originally suggested by Craig

Partridge.  This particular interface originally appeared in the

.Tn INRIA

.Tn IPv6

implementation.

.Sh AUTHORS

Code and documentation by

.An Garrett A. Wollman ,

MIT Laboratory for Computer Science.

.Sh BUGS

The original implementations supported IPv6.  This support should

eventually be resurrected.  The

.Tn NRL

implementation also included support for the

.Dv AF_ISO

and

.Dv AF_NS

address families.

.Pp

The genericity of this interface is somewhat questionable.  A truly

generic interface would provide a means for determining the length of

the buffer to be used so that it could be dynamically allocated, and

would always require a

.Dq Li "struct sockaddr"

to hold the binary address.  Unfortunately, this is incompatible with existing

practice.  This limitation means that a routine for printing network

addresses from arbitrary address families must still have internal

knowledge of the maximum buffer length needed and the appropriate part

of the address to use as the binary address.