path: root/usr/src/man/man3socket/inet.3socket

'\" te
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.TH INET 3SOCKET "Nov 28, 2007"
.SH NAME
inet, inet6, inet_ntop, inet_pton, inet_aton, inet_addr, inet_network,
inet_makeaddr, inet_lnaof, inet_netof, inet_ntoa \- Internet address
manipulation
.SH SYNOPSIS
.LP
.nf
\fBcc\fR [ \fIflag\fR... ] \fIfile\fR... \fB-lsocket\fR \fB -lnsl \fR [ \fIlibrary\fR... ]
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

\fBconst char *\fR\fBinet_ntop\fR(\fBint\fR \fIaf\fR, \fBconst void *\fR\fIaddr\fR, \fBchar *\fR\fIcp\fR,
     \fBsize_t\fR \fIsize\fR);
.fi

.LP
.nf
\fBint\fR \fBinet_pton\fR(\fBint\fR \fIaf\fR, \fBconst char *\fR\fIcp\fR, \fBvoid *\fR\fIaddr\fR);
.fi

.LP
.nf
\fBint\fR \fBinet_aton\fR(\fBconst char *\fR\fIcp\fR, \fBstruct in_addr *\fR\fIaddr\fR);
.fi

.LP
.nf
\fBin_addr_t\fR \fBinet_addr\fR(\fBconst char *\fR\fIcp\fR);
.fi

.LP
.nf
\fBin_addr_t\fR \fBinet_network\fR(\fBconst char *\fR\fIcp\fR);
.fi

.LP
.nf
\fBstruct in_addr\fR \fBinet_makeaddr\fR(\fBconst int\fR \fInet\fR, \fBconst int\fR \fIlna\fR);
.fi

.LP
.nf
\fBint\fR \fBinet_lnaof\fR(\fBconst struct in_addr\fR \fIin\fR);
.fi

.LP
.nf
\fBint\fR \fBinet_netof\fR(\fBconst struct in_addr\fR \fIin\fR);
.fi

.LP
.nf
\fBchar *\fR\fBinet_ntoa\fR(\fBconst struct in_addr\fR \fIin\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBinet_ntop()\fR and \fBinet_pton()\fR functions can manipulate both IPv4
and IPv6 addresses. The \fBinet_aton()\fR, \fBinet_addr()\fR,
\fBinet_network()\fR,  \fBinet_makeaddr()\fR, \fBinet_lnaof()\fR,
\fBinet_netof()\fR, and \fBinet_ntoa()\fR functions can only manipulate IPv4
addresses.
.sp
.LP
The \fBinet_ntop()\fR function converts a numeric address into a string
suitable for presentation. The \fIaf\fR argument specifies the family of the
address which can be \fBAF_INET\fR or \fBAF_INET6\fR. The \fIaddr\fR argument
points to a buffer that holds an IPv4 address if the \fIaf\fR argument is
\fBAF_INET\fR. The \fIaddr\fR argument points to a buffer that holds an IPv6
address if the \fIaf\fR argument is \fBAF_INET6\fR. The address must be in
network byte order. The \fIcp\fR argument points to a buffer where the function
stores the resulting string. The application must specify a non-\fINULL\fR
\fIcp\fR argument. The \fIsize\fR argument specifies the size of this buffer.
For IPv6 addresses, the buffer must be at least 46-octets. For IPv4 addresses,
the buffer must be at least 16-octets. To allow applications to easily declare
buffers of the proper size to store IPv4 and IPv6 addresses in string form, the
following two constants are defined in <\fBnetinet/in.h\fR>:
.sp
.in +2
.nf
#define INET_ADDRSTRLEN    16
#define INET6_ADDRSTRLEN   46
.fi
.in -2

.sp
.LP
The \fBinet_pton()\fR function converts the standard text presentation form of
a function to the numeric binary form. The \fIaf\fR argument specifies the
family of the address. Currently, the \fBAF_INET\fR and \fBAF_INET6\fR address
families are supported. The \fIcp\fR argument points to the string being passed
in. The \fIaddr\fR argument points to a buffer where the function stores the
numeric address. The calling application must ensure that the buffer referred
to by \fIaddr\fR is large enough to hold the numeric address, at least 4 bytes
for \fBAF_INET\fR or 16 bytes for \fBAF_INET6\fR.
.sp
.LP
The \fBinet_aton()\fR, \fBinet_addr()\fR, and \fBinet_network()\fR functions
interpret character strings that represent numbers expressed in the IPv4
standard '\fB\&.\fR' notation, returning numbers suitable for use as IPv4
addresses and IPv4 network numbers, respectively. The \fBinet_makeaddr()\fR
function uses an IPv4 network number and a local network address to construct
an IPv4 address. The \fBinet_netof()\fR and \fBinet_lnaof()\fR functions break
apart IPv4 host addresses, then return the network number and local network
address, respectively.
.sp
.LP
The \fBinet_ntoa()\fR function returns a pointer to a string in the base 256
notation \fBd.d.d.d\fR. See the following section on IPv4 addresses.
.sp
.LP
Internet addresses are returned in network order, bytes ordered from left to
right. Network numbers and local address parts are returned as machine format
integer values.
.SS "IPv6 Addresses"
.sp
.LP
There are three conventional forms for representing IPv6 addresses as strings:
.RS +4
.TP
1.
The preferred form is \fBx:x:x:x:x:x:x:x\fR, where the 'x's are the
hexadecimal values of the eight 16-bit pieces of the address. For example:
.sp
.in +2
.nf
1080:0:0:0:8:800:200C:417A
.fi
.in -2

It is not necessary to write the leading zeros in an individual field. There
must be at least one numeral in every field, except when the special syntax
described in the following is used.
.RE
.RS +4
.TP
2.
It is common for addresses to contain long strings of zero bits in some
methods used to allocate certain IPv6 address styles. A special syntax is
available to compress the zeros. The use of "\fB::\fR" indicates multiple
groups of 16 bits of zeros. The \fB::\fR may only appear once in an address.
The \fB::\fR can also be used to compress the leading and trailing zeros in an
address. For example:
.sp
.in +2
.nf
1080::8:800:200C:417A
.fi
.in -2

.RE
.RS +4
.TP
3.
The alternative form \fBx:x:x:x:x:x:d.d.d.d\fR is sometimes more convenient
when dealing with a mixed environment of IPv4 and IPv6 nodes. The \fBx\fR's in
this form represent the hexadecimal values of the six high-order 16-bit pieces
of the address. The \fBd\fR's represent the decimal values of the four
low-order 8-bit pieces of the standard IPv4 address. For example:
.sp
.in +2
.nf
::FFFF:129.144.52.38
::129.144.52.38
.fi
.in -2

The \fB::FFFF:d.d.d.d\fR and \fB::d.d.d.d\fR pieces are the general forms of an
IPv4-mapped IPv6 address and an IPv4-compatible IPv6 address.
.sp
The IPv4 portion must be in the \fBd.d.d.d\fR form. The following forms are
invalid:
.sp
.in +2
.nf
::FFFF:d.d.d
::FFFF:d.d
::d.d.d
::d.d
.fi
.in -2

The \fB::FFFF:d\fR form is a valid but unconventional representation of the
IPv4-compatible IPv6 address \fB::255.255.0.d\fR.
.sp
The \fB::d\fR form corresponds to the general IPv6 address
\fB0:0:0:0:0:0:0:d\fR.
.RE
.SS "IPv4 Addresses"
.sp
.LP
Values specified using `\fB\&.\fR' notation take one of the following forms:
.sp
.in +2
.nf
d.d.d.d
d.d.d
d.d
d
.fi
.in -2

.sp
.LP
When four parts are specified, each part is interpreted as a byte of data and
assigned from left to right to the four bytes of an IPv4 address.
.sp
.LP
When a three-part address is specified, the last part is interpreted as a
16-bit quantity and placed in the right most two bytes of the network address.
The three part address format is convenient for specifying Class B network
addresses such as \fB128.net.host\fR.
.sp
.LP
When a two-part address is supplied, the last part is interpreted as a 24-bit
quantity and placed in the right most three bytes of the network address. The
two part address format is convenient for specifying Class A network addresses
such as \fBnet.host\fR.
.sp
.LP
When only one part is given, the value is stored directly in the network
address without any byte rearrangement.
.sp
.LP
With the exception of \fBinet_pton()\fR, numbers supplied as \fIparts\fR
in '\fB\&.\fR' notation may be decimal, octal, or hexadecimal, as specified in C
language. For example, a leading \fB0x\fR or \fB0X\fR implies hexadecimal. A
leading \fB0\fR implies octal. Otherwise, the number is interpreted as decimal.
.sp
.LP
For IPv4 addresses, \fBinet_pton()\fR accepts only a string in standard IPv4
dot notation:
.sp
.in +2
.nf
d.d.d.d
.fi
.in -2

.sp
.LP
Each number has one to three digits with a decimal value between 0 and 255.
.sp
.LP
The \fBinet_addr()\fR function has been obsoleted by \fBinet_aton()\fR.
.SH RETURN VALUES
.sp
.LP
The \fBinet_aton()\fR function returns nonzero if the address is valid, \fB0\fR
if the address is invalid.
.sp
.LP
The \fBinet_ntop()\fR function returns a pointer to the buffer that contains a
string if the conversion succeeds. Otherwise, \fINULL\fR is returned. Upon
failure, \fIerrno\fR is set to \fBEAFNOSUPPORT\fR if the \fIaf\fR argument is
invalid or \fBENOSPC\fR if the size of the result buffer is inadequate.
.sp
.LP
The \fBinet_pton()\fR function returns \fB1\fR if the conversion succeeds,
\fB0\fR if the input is not a valid IPv4 dotted-decimal string or a valid  IPv6
address string. The function returns \fB-1\fR with \fIerrno\fR set to
\fBEAFNOSUPPORT\fR if the af argument is unknown.
.sp
.LP
The value \fBINADDR_NONE\fR, which is equivalent to \fB(in_addr_t)(-1)\fR, is
returned by \fBinet_addr()\fR and \fBinet_network()\fR for malformed requests.
.sp
.LP
The functions \fBinet_netof()\fR and \fBinet_lnaof()\fR break apart IPv4 host
addresses, returning the network number and local network address part,
respectively.
.sp
.LP
The function \fBinet_ntoa()\fR returns a pointer to a string in the base 256
notation \fBd.d.d.d\fR, described in the section on IPv4 addresses.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	See below.
_
MT-Level	Safe
.TE

.sp
.LP
The \fBinet_ntop()\fR, \fBinet_pton()\fR, \fBinet_aton()\fR, \fBinet_addr()\fR,
and \fBinet_network()\fR functions are Committed. The \fBinet_lnaof()\fR,
\fBinet_makeaddr()\fR, \fBinet_netof()\fR, and \fBinet_network()\fR functions
are Committed (Obsolete).
.SH SEE ALSO
.sp
.LP
\fBgethostbyname\fR(3NSL), \fBgetipnodebyname\fR(3SOCKET),
\fBgetnetbyname\fR(3SOCKET), \fBinet.h\fR(3HEAD), \fBhosts\fR(4),
\fBnetworks\fR(4), \fBattributes\fR(5)
.SH NOTES
.sp
.LP
The return value from \fBinet_ntoa()\fR points to a buffer which is overwritten
on each call. This buffer is implemented as thread-specific data in
multithreaded applications.
.sp
.LP
IPv4-mapped addresses are not recommended.
.SH BUGS
.sp
.LP
The problem of host byte ordering versus network byte ordering is confusing. A
simple way to specify Class C network addresses in a manner similar to that for
Class B and Class A is needed.