inet_net_pton(3) - Linux manual page (original) (raw)
inetnetpton(3) Library Functions Manual inetnetpton(3)
NAME top
inet_net_pton, inet_net_ntop - Internet network number conversionLIBRARY top
Resolver library (_libresolv_, _-lresolv_)SYNOPSIS top
**#include <arpa/inet.h>**
**int inet_net_pton(int** _af_**, const char ***_pres_**,**
**void** _netp_**[.**_nsize_**], size_t** _nsize_**);**
**char *inet_net_ntop(int** _af_**,**
**const void** _netp_**[(.**_bits_ **- CHAR_BIT + 1) / CHAR_BIT],**
**int** _bits_**,**
**char** _pres_**[.**_psize_**], size_t** _psize_**);**Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
**inet_net_pton**(), **inet_net_ntop**():
Since glibc 2.20:
_DEFAULT_SOURCE
Before glibc 2.20:
_BSD_SOURCE || _SVID_SOURCEDESCRIPTION top
These functions convert network numbers between presentation
(i.e., printable) format and network (i.e., binary) format.
For both functions, _af_ specifies the address family for the
conversion; the only supported value is **AF_INET**.inet_net_pton() The inet_net_pton() function converts pres, a null-terminated string containing an Internet network number in presentation format to network format. The result of the conversion, which is in network byte order, is placed in the buffer pointed to by netp. (The netp argument typically points to an inaddr structure.) The nsize argument specifies the number of bytes available in netp.
On success, **inet_net_pton**() returns the number of bits in the
network number field of the result placed in _netp_. For a
discussion of the input presentation format and the return value,
see NOTES.
_Note_: the buffer pointed to by _netp_ should be zeroed out before
calling **inet_net_pton**(), since the call writes only as many bytes
as are required for the network number (or as are explicitly
specified by _pres_), which may be less than the number of bytes in
a complete network address.inet_net_ntop() The inet_net_ntop() function converts the network number in the buffer pointed to by netp to presentation format; *netp is interpreted as a value in network byte order. The bits argument specifies the number of bits in the network number in *netp.
The null-terminated presentation-format string is placed in the
buffer pointed to by _pres_. The _psize_ argument specifies the
number of bytes available in _pres_. The presentation string is in
CIDR format: a dotted-decimal number representing the network
address, followed by a slash, and the size of the network number
in bits.RETURN VALUE top
On success, **inet_net_pton**() returns the number of bits in the
network number. On error, it returns -1, and _[errno](../man3/errno.3.html)_ is set to
indicate the error.
On success, **inet_net_ntop**() returns _pres_. On error, it returns
NULL, and _[errno](../man3/errno.3.html)_ is set to indicate the error.ERRORS top
**EAFNOSUPPORT**
_af_ specified a value other than **AF_INET**.
**EMSGSIZE**
The size of the output buffer was insufficient.
**ENOENT** (**inet_net_pton**()) _pres_ was not in correct presentation
format.STANDARDS top
None.NOTES top
Input presentation format for inet_net_pton() The network number may be specified either as a hexadecimal value or in dotted-decimal notation.
Hexadecimal values are indicated by an initial "0x" or "0X". The
hexadecimal digits populate the nibbles (half octets) of the
network number from left to right in network byte order.
In dotted-decimal notation, up to four octets are specified, as
decimal numbers separated by dots. Thus, any of the following
forms are accepted:
a.b.c.d
a.b.c
a.b
a
Each part is a number in the range 0 to 255 that populates one
byte of the resulting network number, going from left to right, in
network-byte (big endian) order. Where a part is omitted, the
resulting byte in the network number is zero.
For either hexadecimal or dotted-decimal format, the network
number can optionally be followed by a slash and a number in the
range 0 to 32, which specifies the size of the network number in
bits.Return value of inet_net_pton() The return value of inet_net_pton() is the number of bits in the network number field. If the input presentation string terminates with a slash and an explicit size value, then that size becomes the return value of inet_net_pton(). Otherwise, the return value, bits, is inferred as follows:
• If the most significant byte of the network number is greater
than or equal to 240, then _bits_ is 32.
• Otherwise, if the most significant byte of the network number
is greater than or equal to 224, then _bits_ is 4.
• Otherwise, if the most significant byte of the network number
is greater than or equal to 192, then _bits_ is 24.
• Otherwise, if the most significant byte of the network number
is greater than or equal to 128, then _bits_ is 16.
• Otherwise, _bits_ is 8.
If the resulting _bits_ value from the above steps is greater than
or equal to 8, but the number of octets specified in the network
number exceed _bits/8_, then _bits_ is set to 8 times the number of
octets actually specified.EXAMPLES top
The program below demonstrates the use of **inet_net_pton**() and
**inet_net_ntop**(). It uses **inet_net_pton**() to convert the
presentation format network address provided in its first command-
line argument to binary form, displays the return value from
**inet_net_pton**(). It then uses **inet_net_ntop**() to convert the
binary form back to presentation format, and displays the
resulting string.
In order to demonstrate that **inet_net_pton**() may not write to all
bytes of its _netp_ argument, the program allows an optional second
command-line argument, a number used to initialize the buffer
before **inet_net_pton**() is called. As its final line of output,
the program displays all of the bytes of the buffer returned by
**inet_net_pton**() allowing the user to see which bytes have not been
touched by **inet_net_pton**().
An example run, showing that **inet_net_pton**() infers the number of
bits in the network number:
$ **./a.out 193.168**
inet_net_pton() returned: 24
inet_net_ntop() yielded: 193.168.0/24
Raw address: c1a80000
Demonstrate that **inet_net_pton**() does not zero out unused bytes in
its result buffer:
$ **./a.out 193.168 0xffffffff**
inet_net_pton() returned: 24
inet_net_ntop() yielded: 193.168.0/24
Raw address: c1a800ff
Demonstrate that **inet_net_pton**() will widen the inferred size of
the network number, if the supplied number of bytes in the
presentation string exceeds the inferred value:
$ **./a.out 193.168.1.128**
inet_net_pton() returned: 32
inet_net_ntop() yielded: 193.168.1.128/32
Raw address: c1a80180
Explicitly specifying the size of the network number overrides any
inference about its size (but any extra bytes that are explicitly
specified will still be used by **inet_net_pton**(): to populate the
result buffer):
$ **./a.out 193.168.1.128/24**
inet_net_pton() returned: 24
inet_net_ntop() yielded: 193.168.1/24
Raw address: c1a80180Program source /* Link with "-lresolv" */
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
} while (0)
int
main(int argc, char *argv[])
{
char buf[100];
struct in_addr addr;
int bits;
if (argc < 2) {
fprintf(stderr,
"Usage: %s presentation-form [addr-init-value]\n",
argv[0]);
exit(EXIT_FAILURE);
}
/* If argv[2] is supplied (a numeric value), use it to initialize
the output buffer given to inet_net_pton(), so that we can see
that inet_net_pton() initializes only those bytes needed for
the network number. If argv[2] is not supplied, then initialize
the buffer to zero (as is recommended practice). */
addr.s_addr = (argc > 2) ? strtod(argv[2], NULL) : 0;
/* Convert presentation network number in argv[1] to binary. */
bits = inet_net_pton(AF_INET, argv[1], &addr, sizeof(addr));
if (bits == -1)
errExit("inet_net_ntop");
printf("inet_net_pton() returned: %d\n", bits);
/* Convert binary format back to presentation, using 'bits'
returned by inet_net_pton(). */
if (inet_net_ntop(AF_INET, &addr, bits, buf, sizeof(buf)) == NULL)
errExit("inet_net_ntop");
printf("inet_net_ntop() yielded: %s\n", buf);
/* Display 'addr' in raw form (in network byte order), so we can
see bytes not displayed by inet_net_ntop(); some of those bytes
may not have been touched by inet_net_ntop(), and so will still
have any initial value that was specified in argv[2]. */
printf("Raw address: %x\n", htonl(addr.s_addr));
exit(EXIT_SUCCESS);
}SEE ALSO top
[inet(3)](../man3/inet.3.html), [networks(5)](../man5/networks.5.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 inetnetpton(3)
Pages that refer to this page:inet(3)