addr2ascii, ascii2addr -- Generic address formatting routines
Standard C Library (libc, -lc)
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
char *
addr2ascii(int af, const void *addrp, int len, char *buf);
int
ascii2addr(int af, const char *ascii, void *result);
The routines addr2ascii() and ascii2addr() are used to convert network
addresses between binary form and a printable form appropriate to the
address family. Both functions take an af argument, specifying the
address family to be used in the conversion process. (Currently, only
the AF_INET and AF_LINK address families are supported.)
The addr2ascii() function is used to convert binary, network-format
addresses into printable form. In addition to af, there are three other
arguments. The addrp argument is a pointer to the network address to be
converted. The len argument is the length of the address. The buf argument
is an optional pointer to a caller-allocated buffer to hold the
result; if a null pointer is passed, addr2ascii() uses a statically-allocated
buffer.
The ascii2addr() function performs the inverse operation to addr2ascii().
In addition to af, it takes two arguments, ascii and result. The ascii
argument is a pointer to the string which is to be converted into binary.
The result argument is a pointer to an appropriate network address structure
for the specified family.
The following gives the appropriate structure to use for binary addresses
in the specified family:
AF_INET struct in_addr (in <netinet/in.h>)
AF_LINK struct sockaddr_dl (in <net/if_dl.h>)
The 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 ascii2addr() function returns the length
of the binary address in bytes, or -1 on failure.
The inet(3) functions inet_ntoa() and inet_aton() could be implemented
thusly:
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
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));
}
In actuality, this cannot be done because addr2ascii() and ascii2addr()
are implemented in terms of the inet(3) functions, rather than the other
way around.
When a failure is returned, errno is set to one of the following values:
[ENAMETOOLONG] The addr2ascii() routine was passed a len argument
which was inappropriate for the address family given
by af.
[EPROTONOSUPPORT] Either routine was passed an af argument other than
AF_INET or AF_LINK.
[EINVAL] The string passed to ascii2addr() was improperly formatted
for address family af.
inet(3), linkaddr(3), inet(4)
An interface close to this one was originally suggested by Craig Partridge.
This particular interface originally appeared in the INRIA IPv6
implementation.
Code and documentation by Garrett A. Wollman, MIT Laboratory for Computer
Science.
The original implementations supported IPv6. This support should eventually
be resurrected. The NRL implementation also included support for
the AF_ISO and AF_NS address families.
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 ``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.
FreeBSD 5.2.1 June 13, 1996 FreeBSD 5.2.1 [ Back ] | 