---
name: "inet_net"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["freebsd", "macos"]
url: "https://new.carta.tech/inet_net"
---

# inet\_net(3)

Internet network number manipulation routines

## NAME

**inet\_net\_ntop**, **inet\_net\_pton** – Internet network number manipulation routines

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<arpa/inet.h\>**

*char* *\**\

**inet\_net\_ntop**(*int af*, *const void \*src*, *int bits*, *char \*dst*, *size\_t size*);

*int*\

**inet\_net\_pton**(*int af*, *const char \*src*, *void \*dst*, *size\_t size*);

## DESCRIPTION

The **inet\_net\_ntop**() function converts an Internet network number from network format (usually a *struct in\_addr* or some other binary form, in network byte order) to CIDR presentation format (suitable for external display purposes). The *bits* argument is the number of bits in *src* that are the network number. 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 **inet\_net\_pton**() function converts a presentation format Internet network number (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). It returns the number of bits (either computed based on the class, or specified with /CIDR), or -1 if a failure occurred (in which case *errno* will have been set. It will be set to ENOENT if the Internet network number was not valid).

The currently supported values for *af* are AF\_INET and AF\_INET6. The *size* argument is the size of the result buffer *dst*.

## NETWORK NUMBERS (IP VERSION 4)

Internet network numbers may be specified in one of the following forms:

```
a.b.c.d/bits
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 network number. Note that when an Internet network number is viewed as a 32-bit integer quantity on a system that uses little-endian byte order (such as the Intel 386, 486, and Pentium processors) the bytes referred to above appear as “d.c.b.a”. That is, little-endian bytes are ordered from right to left.

When a three part number is specified, the last part is interpreted as a 16-bit quantity and placed in the rightmost two bytes of the Internet network number. This makes the three part number format convenient for specifying Class B network numbers as “128.net.host”.

When a two part number is supplied, the last part is interpreted as a 24-bit quantity and placed in the rightmost three bytes of the Internet network number. This makes the two part number format convenient for specifying Class A network numbers as “net.host”.

When only one part is given, the value is stored directly in the Internet network number 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).

## LEGACY SYNOPSIS

**#include \<sys/types.h\>** **#include \<sys/socket.h\>** **#include \<netinet/in.h\>** **#include \<arpa/inet.h\>**

These include files were necessary for all functions.

## SEE ALSO

[byteorder(3)](/byteorder/3.md), [inet(3)](/inet/3.md), [networks(5)](/networks/5.md)

## HISTORY

The **inet\_net\_ntop**() and **inet\_net\_pton**() functions appeared in BIND 4.9.4.