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Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" From: @(#)inet.3 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD$ 34.\" 35.Dd June 14, 2004 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 80The routines 81.Fn inet_aton , 82.Fn inet_addr 83and 84.Fn inet_network 85interpret character strings representing 86numbers expressed in the Internet standard 87.Ql .\& 88notation. 89.Pp 90The 91.Fn inet_pton 92function converts a presentation format address (that is, printable form 93as held in a character string) to network format (usually a 94.Ft struct in_addr 95or some other internal binary representation, in network byte order). 96It returns 1 if the address was valid for the specified address family, or 970 if the address wasn't parseable in the specified address family, or -1 98if some system error occurred (in which case 99.Va errno 100will have been set). 101This function is presently valid for 102.Dv AF_INET 103and 104.Dv AF_INET6 . 105.Pp 106The 107.Fn inet_aton 108routine interprets the specified character string as an Internet address, 109placing the address into the structure provided. 110It returns 1 if the string was successfully interpreted, 111or 0 if the string is invalid. 112The 113.Fn inet_addr 114and 115.Fn inet_network 116functions return numbers suitable for use 117as Internet addresses and Internet network 118numbers, respectively. 119.Pp 120The function 121.Fn inet_ntop 122converts an address 123.Fa *src 124from network format 125(usually a 126.Ft struct in_addr 127or some other binary form, in network byte order) to presentation format 128(suitable for external display purposes). 129The 130.Fa size 131argument specifies the size, in bytes, of the buffer 132.Fa *dst . 133It returns NULL if a system error occurs (in which case, 134.Va errno 135will have been set), or it returns a pointer to the destination string. 136This function is presently valid for 137.Dv AF_INET 138and 139.Dv AF_INET6 . 140.Pp 141The routine 142.Fn inet_ntoa 143takes an Internet address and returns an 144.Tn ASCII 145string representing the address in 146.Ql .\& 147notation. The routine 148.Fn inet_makeaddr 149takes an Internet network number and a local 150network address and constructs an Internet address 151from it. The routines 152.Fn inet_netof 153and 154.Fn inet_lnaof 155break apart Internet host addresses, returning 156the network number and local network address part, 157respectively. 158.Pp 159All Internet addresses are returned in network 160order (bytes ordered from left to right). 161All network numbers and local address parts are 162returned as machine byte order integer values. 163.Sh INTERNET ADDRESSES 164Values specified using the 165.Ql .\& 166notation take one 167of the following forms: 168.Bd -literal -offset indent 169a.b.c.d 170a.b.c 171a.b 172a 173.Ed 174.Pp 175When four parts are specified, each is interpreted 176as a byte of data and assigned, from left to right, 177to the four bytes of an Internet address. Note 178that when an Internet address is viewed as a 32-bit 179integer quantity on the 180.Tn VAX 181the bytes referred to 182above appear as 183.Dq Li d.c.b.a . 184That is, 185.Tn VAX 186bytes are 187ordered from right to left. 188.Pp 189When a three part address is specified, the last 190part is interpreted as a 16-bit quantity and placed 191in the right-most two bytes of the network address. 192This makes the three part address format convenient 193for specifying Class B network addresses as 194.Dq Li 128.net.host . 195.Pp 196When a two part address is supplied, the last part 197is interpreted as a 24-bit quantity and placed in 198the right most three bytes of the network address. 199This makes the two part address format convenient 200for specifying Class A network addresses as 201.Dq Li net.host . 202.Pp 203When only one part is given, the value is stored 204directly in the network address without any byte 205rearrangement. 206.Pp 207All numbers supplied as 208.Dq parts 209in a 210.Ql .\& 211notation 212may be decimal, octal, or hexadecimal, as specified 213in the C language (i.e., a leading 0x or 0X implies 214hexadecimal; otherwise, a leading 0 implies octal; 215otherwise, the number is interpreted as decimal). 216.Pp 217The 218.Fn inet_aton 219and 220.Fn inet_ntoa 221functions are semi-deprecated in favor of the 222.Xr addr2ascii 3 223family. However, since those functions are not yet widely implemented, 224portable programs cannot rely on their presence and will continue 225to use the 226.Xr inet 3 227functions for some time. 228.Sh DIAGNOSTICS 229The constant 230.Dv INADDR_NONE 231is returned by 232.Fn inet_addr 233and 234.Fn inet_network 235for malformed requests. 236.Sh ERRORS 237The 238.Fn inet_ntop 239call fails if: 240.Bl -tag -width Er 241.It Bq Er ENOSPC 242.Fa size 243was not large enough to store the presentation form of the address. 244.It Bq Er EAFNOSUPPORT 245.Fa *src 246was not an 247.Dv AF_INET 248or 249.Dv AF_INET6 250family address. 251.El 252.Sh SEE ALSO 253.Xr addr2ascii 3 , 254.Xr byteorder 3 , 255.Xr gethostbyname 3 , 256.Xr getnetent 3 , 257.Xr inet_net 3 , 258.Xr hosts 5 , 259.Xr networks 5 260.Rs 261.%R RFC 262.%N 2373 263.%D July 1998 264.%T "IP Version 6 Addressing Architecture" 265.Re 266.Sh STANDARDS 267The 268.Fn inet_ntop 269and 270.Fn inet_pton 271functions conform to 272.St -xns5.2 . 273Note that 274.Fn inet_pton 275does not accept 1-, 2-, or 3-part dotted addresses; all four parts 276must be specified and are interpreted only as decimal values. 277This is a narrower input set than that accepted by 278.Fn inet_aton . 279.Sh HISTORY 280These 281functions appeared in 282.Bx 4.2 . 283.Sh BUGS 284The value 285.Dv INADDR_NONE 286(0xffffffff) is a valid broadcast address, but 287.Fn inet_addr 288cannot return that value without indicating failure. 289The newer 290.Fn inet_aton 291function does not share this problem. 292The problem of host byte ordering versus network byte ordering is 293confusing. 294The string returned by 295.Fn inet_ntoa 296resides in a static memory area. 297.Pp 298Inet_addr should return a 299.Fa struct in_addr . 300