ADDR2ASCII(3) | Library Functions Manual | ADDR2ASCII(3) |
addr2ascii
,
ascii2addr
— Generic address
formatting routines
Standard C Library (libc, -lc)
#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
<arpa/inet.h>
)AF_LINK
struct
sockaddr_dl
(in
<net/if_dl.h>
)AF_INET and AF_LINK constants are defined
in
<sys/socket.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/socket.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
]addr2ascii
() routine was passed a
len argument which was inappropriate for the address
family given by af.EPROTONOSUPPORT
]AF_INET
or AF_LINK
.EINVAL
]ascii2addr
() was improperly
formatted for address family af.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.
June 13, 1996 | macOS 14.6 |