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49 >eCos Reference Manual</TH
57 HREF="net-common-tcpip-manpages-if-nametoindex.html"
65 >Chapter 38. TCP/IP Library Reference</TD
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85 NAME="NET-COMMON-TCPIP-MANPAGES-INET">inet</H1
94 >INET(3) System Library Functions Manual INET(3)
97 inet_addr, inet_aton, inet_lnaof, inet_makeaddr, inet_netof,
98 inet_network, inet_ntoa, inet_ntop, inet_pton - Internet address manipu-
102 #include <sys/socket.h>
103 #include <netinet/in.h>
104 #include <arpa/inet.h>
107 inet_addr(const char *cp);
110 inet_aton(const char *cp, struct in_addr *addr);
113 inet_lnaof(struct in_addr in);
116 inet_makeaddr(unsigned long net, unsigned long lna);
119 inet_netof(struct in_addr in);
122 inet_network(const char *cp);
125 inet_ntoa(struct in_addr in);
128 inet_ntop(int af, const void *src, char *dst, size_t size);
131 inet_pton(int af, const char *src, void *dst);
134 The routines inet_aton(), inet_addr() and inet_network() interpret char-
135 acter strings representing numbers expressed in the Internet standard `.'
136 notation. The inet_pton() function converts a presentation format
137 address (that is, printable form as held in a character string) to net-
138 work format (usually a struct in_addr or some other internal binary rep-
139 resentation, in network byte order). It returns 1 if the address was
140 valid for the specified address family, or 0 if the address wasn't
141 parseable in the specified address family, or -1 if some system error
142 occurred (in which case errno will have been set). This function is
143 presently valid for AF_INET and AF_INET6. The inet_aton() routine inter-
144 prets the specified character string as an Internet address, placing the
145 address into the structure provided. It returns 1 if the string was suc-
146 cessfully interpreted, or 0 if the string was invalid. The inet_addr()
147 and inet_network() functions return numbers suitable for use as Internet
148 addresses and Internet network numbers, respectively.
150 The function inet_ntop() converts an address from network format (usually
151 a struct in_addr or some other binary form, in network byte order) to
152 presentation format (suitable for external display purposes). It returns
153 NULL if a system error occurs (in which case, errno will have been set),
154 or it returns a pointer to the destination string. The routine
155 inet_ntoa() takes an Internet address and returns an ASCII string repre-
156 senting the address in `.' notation. The routine inet_makeaddr() takes
157 an Internet network number and a local network address and constructs an
158 Internet address from it. The routines inet_netof() and inet_lnaof()
159 break apart Internet host addresses, returning the network number and
160 local network address part, respectively.
162 All Internet addresses are returned in network order (bytes ordered from
163 left to right). All network numbers and local address parts are returned
164 as machine format integer values.
166 INTERNET ADDRESSES (IP VERSION 4)
167 Values specified using the `.' notation take one of the following forms:
174 When four parts are specified, each is interpreted as a byte of data and
175 assigned, from left to right, to the four bytes of an Internet address.
176 Note that when an Internet address is viewed as a 32-bit integer quantity
177 on a system that uses little-endian byte order (such as the Intel 386,
178 486 and Pentium processors) the bytes referred to above appear as
179 ``d.c.b.a''. That is, little-endian bytes are ordered from right to
182 When a three part address is specified, the last part is interpreted as a
183 16-bit quantity and placed in the rightmost two bytes of the network
184 address. This makes the three part address format convenient for speci-
185 fying Class B network addresses as ``128.net.host''.
187 When a two part address is supplied, the last part is interpreted as a
188 24-bit quantity and placed in the rightmost three bytes of the network
189 address. This makes the two part address format convenient for specify-
190 ing Class A network addresses as ``net.host''.
192 When only one part is given, the value is stored directly in the network
193 address without any byte rearrangement.
195 All numbers supplied as ``parts'' in a `.' notation may be decimal,
196 octal, or hexadecimal, as specified in the C language (i.e., a leading 0x
197 or 0X implies hexadecimal; otherwise, a leading 0 implies octal; other-
198 wise, the number is interpreted as decimal).
200 INTERNET ADDRESSES (IP VERSION 6)
201 In order to support scoped IPv6 addresses, getaddrinfo(3) and
202 getnameinfo(3) are recommended rather than the functions presented here.
204 The presentation format of an IPv6 address is given in [RFC1884 2.2]:
206 There are three conventional forms for representing IPv6 addresses as
209 1. The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the hex-
210 adecimal values of the eight 16-bit pieces of the address. Exam-
213 FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
214 1080:0:0:0:8:800:200C:417A
216 Note that it is not necessary to write the leading zeros in an indi-
217 vidual field, but there must be at least one numeral in every field
218 (except for the case described in 2.).
220 2. Due to the method of allocating certain styles of IPv6 addresses, it
221 will be common for addresses to contain long strings of zero bits.
222 In order to make writing addresses
224 containing zero bits easier a special syntax is available to com-
225 press the zeros. The use of ``::'' indicates multiple groups of 16
226 bits of zeros. The ``::'' can only appear once in an address. The
227 ``::'' can also be used to compress the leading and/or trailing
230 For example the following addresses:
232 1080:0:0:0:8:800:200C:417A a unicast address
233 FF01:0:0:0:0:0:0:43 a multicast address
234 0:0:0:0:0:0:0:1 the loopback address
235 0:0:0:0:0:0:0:0 the unspecified addresses
237 may be represented as:
239 1080::8:800:200C:417A a unicast address
240 FF01::43 a multicast address
241 ::1 the loopback address
242 :: the unspecified addresses
244 3. An alternative form that is sometimes more convenient when dealing
245 with a mixed environment of IPv4 and IPv6 nodes is
246 x:x:x:x:x:x:d.d.d.d, where the 'x's are the hexadecimal values of
247 the six high-order 16-bit pieces of the address, and the 'd's are
248 the decimal values of the four low-order 8-bit pieces of the address
249 (standard IPv4 representation). Examples:
251 0:0:0:0:0:0:13.1.68.3
252 0:0:0:0:0:FFFF:129.144.52.38
254 or in compressed form:
260 The constant INADDR_NONE is returned by inet_addr() and inet_network()
261 for malformed requests.
264 byteorder(3), gethostbyname(3), getnetent(3), inet_net(3), hosts(5),
268 The inet_ntop and inet_pton functions conforms to the IETF IPv6 BSD API
269 and address formatting specifications. Note that inet_pton does not
270 accept 1-, 2-, or 3-part dotted addresses; all four parts must be speci-
271 fied. This is a narrower input set than that accepted by inet_aton.
274 The inet_addr, inet_network, inet_makeaddr, inet_lnaof and inet_netof
275 functions appeared in 4.2BSD. The inet_aton and inet_ntoa functions
276 appeared in 4.3BSD. The inet_pton and inet_ntop functions appeared in
280 The value INADDR_NONE (0xffffffff) is a valid broadcast address, but
281 inet_addr() cannot return that value without indicating failure. Also,
282 inet_addr() should have been designed to return a struct in_addr. The
283 newer inet_aton() function does not share these problems, and almost all
284 existing code should be modified to use inet_aton() instead.
286 The problem of host byte ordering versus network byte ordering is confus-
289 The string returned by inet_ntoa() resides in a static memory area.
291 BSD June 18, 1997 BSD
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355 >inet6_option_space</TD