inet_ntop

, inet_pton

- convert IPv4 and IPv6 addresses between binary and text form

Synopsis

cc [ flag ... ] file ... -lxnet [ library ... ]
#include <arpa/inet.h>

const char *inet_ntop(int af, const void *restrict src,
     char *restrict dst, socklen_t size);

int inet_pton(int af, const char *restrict src, dst);

Description

The inet_ntop() function converts a numeric address into a text string suitable for presentation. 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 stores the resulting text string; it cannot 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).

The inet_pton() function converts an address in its standard text presentation form into its numeric binary form. The af argument specifies the family of the address. The AF_INET and AF_INET6 address families are supported. The src argument points to the string being passed in. The dst argument points to a buffer into which the function stores the numeric address; this must be large enough to hold the numeric address (32 bits for AF_INET, 128 bits for AF_INET6).

If the af argument of inet_pton() is AF_INET, the src string is in the standard IPv4 dotted-decimal form:

ddd.ddd.ddd.ddd

where “ddd”is a one to three digit decimal number between 0 and 255 (see inet_addr(3XNET)). The inet_pton() function does not accept other formats (such as the octal numbers, hexadecimal numbers, and fewer than four numbers that inet_addr() accepts).

If the af argument of inet_pton() is AF_INET6, the src string is 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”) can 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).

A more extensive description of the standard representations of IPv6 addresses can be found in RFC 2373.

Return Values

The inet_ntop() function returns a pointer to the buffer containing the text string if the conversion succeeds. Otherwise it returns NULL and sets errno to indicate the error.

The inet_pton() function returns 1 if the conversion succeeds, with the address pointed to by dst in network byte order. It returns 0 if the input is not a valid IPv4 dotted-decimal string or a valid IPv6 address string. It returns -1 and sets errno to EAFNOSUPPORT if the af argument is unknown.

Errors

The inet_ntop() and inet_pton() functions will fail if:

EAFNOSUPPORT

The af argument is invalid.

ENOSPC

The size of the inet_ntop() result buffer is inadequate.

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

inet_addr(3XNET), attributes(5)