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29 .\" $ANA: addr2ascii.3,v 1.1 1996/06/13 18:41:46 wollman Exp $
30 .\" $FreeBSD: src/lib/libc/net/addr2ascii.3,v 1.7.2.5 2001/12/14 18:33:55 ru Exp $
38 .Nd Generic address formatting routines
46 .Fn addr2ascii "int af" "const void *addrp" "int len" "char *buf"
48 .Fn ascii2addr "int af" "const char *ascii" "void *result"
54 are used to convert network addresses between binary form and a
55 printable form appropriate to the address family. Both functions take
58 argument, specifying the address family to be used in the conversion
64 address families are supported.)
69 is used to convert binary, network-format addresses into printable
72 there are three other arguments. The
74 argument is a pointer to the network address to be converted.
77 argument is the length of the address. The
79 argument is an optional pointer to a caller-allocated buffer to hold
80 the result; if a null pointer is passed,
82 uses a statically-allocated buffer.
86 function performs the inverse operation to
90 it takes two parameters,
96 parameter is a pointer to the string which is to be converted into
99 parameter is a pointer to an appropriate network address structure for
100 the specified family.
102 The following gives the appropriate structure to use for binary
103 addresses in the specified family:
105 .Bl -tag -width AF_INETxxxx -compact
109 .Aq Pa netinet/in.h )
111 .Li struct sockaddr_dl
115 .\" .Li struct in6_addr
117 .\" .Aq Pa netinet6/in6.h )
122 function returns the address of the buffer it was passed, or a static
123 buffer if the a null pointer was passed; on failure, it returns a null
127 function returns the length of the binary address in bytes, or -1 on
136 could be implemented thusly:
137 .Bd -literal -offset indent
138 #include <sys/types.h>
139 #include <sys/socket.h>
140 #include <netinet/in.h>
141 #include <arpa/inet.h>
144 inet_ntoa(struct in_addr addr)
146 return addr2ascii(AF_INET, &addr, sizeof addr, 0);
150 inet_aton(const char *ascii, struct in_addr *addr)
152 return (ascii2addr(AF_INET, ascii, addr)
157 In actuality, this cannot be done because
161 are implemented in terms of the
163 functions, rather than the other way around.
165 When a failure is returned,
167 is set to one of the following values:
169 .It Bq Er ENAMETOOLONG
174 parameter which was inappropriate for the address family given by
176 .It Bq Er EPROTONOSUPPORT
177 Either routine was passed an
186 was improperly formatted for address family
194 An interface close to this one was originally suggested by Craig
195 Partridge. This particular interface originally appeared in the
200 Code and documentation by
201 .An Garrett A. Wollman ,
202 MIT Laboratory for Computer Science.
204 The original implementations supported IPv6. This support should
205 eventually be resurrected. The
207 implementation also included support for the
213 The genericity of this interface is somewhat questionable. A truly
214 generic interface would provide a means for determining the length of
215 the buffer to be used so that it could be dynamically allocated, and
216 would always require a
217 .Dq Li "struct sockaddr"
218 to hold the binary address. Unfortunately, this is incompatible with existing
219 practice. This limitation means that a routine for printing network
220 addresses from arbitrary address families must still have internal
221 knowledge of the maximum buffer length needed and the appropriate part
222 of the address to use as the binary address.