INET(3N)INET(3N)NAME
inet_aton, inet_addr, inet_network, inet_isaddr, inet_ntoa, inet_ntop,
inet_pton, inet_makeaddr, inet_lnaof, inet_netof - Internet address
manipulation routines
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
int inet_aton(const char *cp, struct in_addr *pin);
unsigned long inet_addr(const char *cp);
unsigned long inet_network(const char *cp);
int inet_isaddr(const char *cp, uint32_t *addr);
char *inet_ntoa(struct in_addr in);
const char *inet_ntop(int af, const void *src, char *dst, socklen_t size);
int inet_pton(int af, const char *src, void *dst);
struct in_addr inet_makeaddr(int net, int lna);
unsigned long inet_lnaof(struct in_addr in);
unsigned long inet_netof(struct in_addr in);
DESCRIPTION
The routines inet_aton, inet_addr and inet_network interpret character
strings representing numbers expressed in the Internet standard "." (dot)
notation.
The inet_pton function converts a presentation format address (that is,
printable form as held in a character string) to network format (usually
a struct in_addr or some other internal binary representation, in network
byte order). The function returns 1 if the address is valid or 0 if it
could not be parsed for the given address family. If the af argument is
unknown, then -1 is returned with errno set to EAFNOSUPPORT. This
function is presently valid for AF_INET and AF_INET6. The following
discussion under INTERNET ADDRESSES is not valid for the function
inet_pton , because if its af argument is AF_INET then the src string can
be only in the standard IPv4 dotted decimal form:
ddd.ddd.ddd.ddd
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where 'ddd' is a one to three digit decimal number between 0 and 255 (see
the inet_addr() definition). The inet_pton () function does not accept
other formats (such as the octal numbers, hexadecimal numbers, and fewer
than four numbers that inet_aton () or inet_addr () accepts). This is a
narrower input set than that accepted by inet_aton.
If the af argument of inet_pton () is AF_INET6, the src string must be in
one of the following standard IPv6 text forms:
1. The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the
hexadecimal values of the eight 16-bit pieces of the address.
Leading zeros in individual fields can be omitted, but there must be
at least one numeral in every field.
2. A string of contiguous zero fields in the preferred form can be
shown as "::". The "::" can only appear once in an address.
Unspecified addresses (0:0:0:0:0:0:0:0) may be represented simply as
"::".
3. A third form that is sometimes more convenient when dealing with a
mixed environment of IPv4 and IPv6 nodes is x:x:x:x:x:x:d.d.d.d,
where the "x"s are the hexadecimal values of the six high-order 16-
bit pieces of the address, and the "d"s are the decimal values of
the four low-order 8-bit pieces of the address (standard IPv4
representation).
The inet_aton routine interprets the specified character string as an
Internet address, placing the address into the structure provided. It
returns 1 if the string was successfully interpreted, or 0 if the string
is invalid. The inet_addr and inet_network functions return numbers
suitable for use as Internet addresses and Internet network numbers,
respectively.
The function inet_ntop converts an address from network format (usually a
struct in_addr or some other binary form, in network byte order) to
presentation format (suitable for external display purposes). It returns
NULL if a system error occurs (in which case, errno will have been set),
or it returns a pointer to the destination string. The af argument
specifies the family of the address. This can be AF_INET or AF_INET6.
The src argument points to a buffer holding an IPv4 address if the af
argument is AF_INET, or an IPv6 address if the af argument is AF_INET6.
The dst argument points to a buffer where the function will store the
resulting text string; it must not be NULL. The size argument specifies
the size of this buffer, which must be large enough to hold the text
string(INET_ADDRSTRLEN characters for IPv4, INET6_ADDRSTRLEN characters
for IPv6).
To determine if an ASCII string is a valid representation of an IPv4
address, the function inet_isaddr may be used. It takes a pointer to the
string, cp, and returns a 1 if the address is valid, 0 otherwise.
Additionally, if the addr parameter is non-NULL, the converted address
will be stored at the address pointed to by addr.
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The routine inet_ntoa takes an Internet address and returns an ASCII
string representing the address in "." notation. The routine
inet_makeaddr takes an Internet network number and a local network
address and constructs an Internet address from it. The routines
inet_netof and inet_lnaof break apart Internet host addresses, returning
the network number and local network address part, respectively.
All Internet addresses are returned in network order (bytes ordered from
left to right). All network numbers and local address parts are returned
as machine format integer values.
INTERNET ADDRESSES
Values specified using the "." notation take one of the following forms:
a.b.c.d
a.b.c
a.b
a
When four parts are specified, each is interpreted as a byte of data and
assigned, from left to right, to the four bytes of an Internet address.
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. This makes the three part address format convenient for
specifying Class B network addresses as "128.net.host".
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. This makes the two part address format convenient for
specifying Class A network addresses as "net.host".
When only one part is given, the value is stored directly in the network
address without any byte rearrangement.
All numbers supplied as "parts" in a "." notation may be decimal, octal,
or hexadecimal, as specified in the C language (i.e., a leading 0x or 0X
implies hexadecimal; otherwise, a leading 0 implies octal; otherwise, the
number is interpreted as decimal).
DIAGNOSTICS
The constant INADDR_NONE is returned by inet_addr and inet_network for
malformed requests.
SEE ALSOgethostbyname(3N), getnetent(3N), hosts(4), networks(4)STANDARDS
The inet_ntop and inet_pton functions conform to XNS 5.2 standards.
BUGS
The value INADDR_NONE (0xffffffff) is a valid broadcast address, but
inet_addr cannot return that value without indicating failure. The newer
inet_aton function does not share this problem.
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The string returned by inet_ntoa resides in a static memory area. Thus
printf("%s %s0, inet_ntoa(addr1), inet_ntoa(addr2));
will print the same address twice.
Inet_addr should return a struct in_addr.
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.
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