net/FreeBSD/inet.3

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  32 .\"     From: @(#)inet.3        8.1 (Berkeley) 6/4/93
  33 .\" $FreeBSD: src/lib/libc/net/inet.3,v 1.25 2002/09/06 11:23:49 tjr Exp $
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  35 .Dd June 17, 1996
  36 .Dt INET 3
  37 .Os
  38 .Sh NAME
  39 .Nm inet_aton ,
  40 .Nm inet_addr ,
  41 .Nm inet_network ,
  42 .Nm inet_ntoa ,
  43 .Nm inet_ntop ,
  44 .Nm inet_pton ,
  45 .Nm inet_makeaddr ,
  46 .Nm inet_lnaof ,
  47 .Nm inet_netof
  48 .Nd Internet address manipulation routines
  49 .Sh LIBRARY
  50 .Lb libc
  51 .Sh SYNOPSIS
  52 .In sys/types.h
  53 .In sys/socket.h
  54 .In netinet/in.h
  55 .In arpa/inet.h
  56 .Ft int
  57 .Fn inet_aton "const char *cp" "struct in_addr *pin"
  58 .Ft in_addr_t
  59 .Fn inet_addr "const char *cp"
  60 .Ft in_addr_t
  61 .Fn inet_network "const char *cp"
  62 .Ft char *
  63 .Fn inet_ntoa "struct in_addr in"
  64 .Ft const char *
  65 .Fo inet_ntop
  66 .Fa "int af"
  67 .Fa "const void * restrict src"
  68 .Fa "char * restrict dst"
  69 .Fa "socklen_t size"
  70 .Fc
  71 .Ft int
  72 .Fn inet_pton "int af" "const char * restrict src" "void * restrict dst"
  73 .Ft struct in_addr
  74 .Fn inet_makeaddr "in_addr_t net" "in_addr_t lna"
  75 .Ft in_addr_t
  76 .Fn inet_lnaof "struct in_addr in"
  77 .Ft in_addr_t
  78 .Fn inet_netof "struct in_addr in"
  79 .Sh DESCRIPTION
  80 The routines
  81 .Fn inet_aton ,
  82 .Fn inet_addr
  83 and
  84 .Fn inet_network
  85 interpret character strings representing
  86 numbers expressed in the Internet standard
  87 .Ql .\&
  88 notation.
  89 .Pp
  90 The
  91 .Fn inet_pton
  92 function converts a presentation format address (that is, printable form
  93 as held in a character string) to network format (usually a
  94 .Ft struct in_addr
  95 or some other internal binary representation, in network byte order).
  96 It returns 1 if the address was valid for the specified address family, or
  97 0 if the address wasn't parseable in the specified address family, or -1
  98 if some system error occurred (in which case
  99 .Va errno
 100 will have been set).
 101 This function is presently valid for
 102 .Dv AF_INET
 103 and
 104 .Dv AF_INET6 .
 105 .Pp
 106 The
 107 .Fn inet_aton
 108 routine interprets the specified character string as an Internet address,
 109 placing the address into the structure provided.
 110 It returns 1 if the string was successfully interpreted,
 111 or 0 if the string is invalid.
 112 The
 113 .Fn inet_addr
 114 and
 115 .Fn inet_network
 116 functions return numbers suitable for use
 117 as Internet addresses and Internet network
 118 numbers, respectively.
 119 .Pp
 120 The function
 121 .Fn inet_ntop
 122 converts an address from network format (usually a
 123 .Ft struct in_addr
 124 or some other binary form, in network byte order) to presentation format
 125 (suitable for external display purposes).
 126 It returns NULL if a system error occurs (in which case,
 127 .Va errno
 128 will have been set), or it returns a pointer to the destination string.
 129 This function is presently valid for
 130 .Dv AF_INET
 131 and
 132 .Dv AF_INET6 .
 133 .Pp
 134 The routine
 135 .Fn inet_ntoa
 136 takes an Internet address and returns an
 137 .Tn ASCII
 138 string representing the address in
 139 .Ql .\&
 140 notation.  The routine
 141 .Fn inet_makeaddr
 142 takes an Internet network number and a local
 143 network address and constructs an Internet address
 144 from it.  The routines
 145 .Fn inet_netof
 146 and
 147 .Fn inet_lnaof
 148 break apart Internet host addresses, returning
 149 the network number and local network address part,
 150 respectively.
 151 .Pp
 152 All Internet addresses are returned in network
 153 order (bytes ordered from left to right).
 154 All network numbers and local address parts are
 155 returned as machine byte order integer values.
 156 .Sh INTERNET ADDRESSES
 157 Values specified using the
 158 .Ql .\&
 159 notation take one
 160 of the following forms:
 161 .Bd -literal -offset indent
 162 a.b.c.d
 163 a.b.c
 164 a.b
 165 a
 166 .Ed
 167 .Pp
 168 When four parts are specified, each is interpreted
 169 as a byte of data and assigned, from left to right,
 170 to the four bytes of an Internet address.  Note
 171 that when an Internet address is viewed as a 32-bit
 172 integer quantity on the
 173 .Tn VAX
 174 the bytes referred to
 175 above appear as
 176 .Dq Li d.c.b.a .
 177 That is,
 178 .Tn VAX
 179 bytes are
 180 ordered from right to left.
 181 .Pp
 182 When a three part address is specified, the last
 183 part is interpreted as a 16-bit quantity and placed
 184 in the right-most two bytes of the network address.
 185 This makes the three part address format convenient
 186 for specifying Class B network addresses as
 187 .Dq Li 128.net.host .
 188 .Pp
 189 When a two part address is supplied, the last part
 190 is interpreted as a 24-bit quantity and placed in
 191 the right most three bytes of the network address.
 192 This makes the two part address format convenient
 193 for specifying Class A network addresses as
 194 .Dq Li net.host .
 195 .Pp
 196 When only one part is given, the value is stored
 197 directly in the network address without any byte
 198 rearrangement.
 199 .Pp
 200 All numbers supplied as
 201 .Dq parts
 202 in a
 203 .Ql .\&
 204 notation
 205 may be decimal, octal, or hexadecimal, as specified
 206 in the C language (i.e., a leading 0x or 0X implies
 207 hexadecimal; otherwise, a leading 0 implies octal;
 208 otherwise, the number is interpreted as decimal).
 209 .Pp
 210 The
 211 .Fn inet_aton
 212 and
 213 .Fn inet_ntoa
 214 functions are semi-deprecated in favor of the
 215 .Xr addr2ascii 3
 216 family.  However, since those functions are not yet widely implemented,
 217 portable programs cannot rely on their presence and will continue
 218 to use the
 219 .Xr inet 3
 220 functions for some time.
 221 .Sh DIAGNOSTICS
 222 The constant
 223 .Dv INADDR_NONE
 224 is returned by
 225 .Fn inet_addr
 226 and
 227 .Fn inet_network
 228 for malformed requests.
 229 .Sh SEE ALSO
 230 .Xr addr2ascii 3 ,
 231 .Xr byteorder 3 ,
 232 .Xr gethostbyname 3 ,
 233 .Xr getnetent 3 ,
 234 .Xr inet_net 3 ,
 235 .Xr hosts 5 ,
 236 .Xr networks 5
 237 .Rs
 238 .%R RFC
 239 .%N 2373
 240 .%D July 1998
 241 .%T "IP Version 6 Addressing Architecture"
 242 .Re
 243 .Sh STANDARDS
 244 The
 245 .Fn inet_ntop
 246 and
 247 .Fn inet_pton
 248 functions conform to
 249 .St -xns5.2 .
 250 Note that
 251 .Fn inet_pton
 252 does not accept 1-, 2-, or 3-part dotted addresses; all four parts
 253 must be specified and are interpreted only as decimal values.
 254 This is a narrower input set than that accepted by
 255 .Fn inet_aton .
 256 .Sh HISTORY
 257 These
 258 functions appeared in
 259 .Bx 4.2 .
 260 .Sh BUGS
 261 The value
 262 .Dv INADDR_NONE
 263 (0xffffffff) is a valid broadcast address, but
 264 .Fn inet_addr
 265 cannot return that value without indicating failure.
 266 The newer
 267 .Fn inet_aton
 268 function does not share this problem.
 269 The problem of host byte ordering versus network byte ordering is
 270 confusing.
 271 The string returned by
 272 .Fn inet_ntoa
 273 resides in a static memory area.
 274 .Pp
 275 Inet_addr should return a
 276 .Fa struct in_addr .