Values specified using the . notation take one of the following forms:
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. Note that when an Internet address is viewed as a 32-bit integer quantity on the VAX the bytes referred to above appear as "d.c.b.a". That is, VAX bytes are ordered from right to left.
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).
The inet_aton and inet_ntoa functions are semi-deprecated in favor of the addr2ascii(3) family. However, since those functions are not yet widely implemented, portable programs cannot rely on their presence and will continue to use the inet(3) functions for some time.
The constant INADDR_NONE is returned by inet_addr and inet_network for malformed requests.
The inet_ntop call fails if: