inet_aton(), inet_addr(), inet_network(), inet_ntoa(), inet_makeaddr(), inet_lnaof(), inet_netof() - Internet address manipulation routines
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
int inet_aton (char *cp, struct in_addr *pin)
unsigned long inet_addr (char *cp)
unsigned long inet_network (char *cp)
char * inet_ntoa (struct in_addr in)
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)
The routines inet_aton(3), inet_addr(3) and inet_network(3) interpret character strings
representing numbers expressed in the Internet standard
. notation. The inet_aton(3) 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(3) and inet_network(3) functions
return numbers suitable for use as Internet addresses and Internet
network numbers, respectively. The routine inet_ntoa(3) takes an
Internet address and returns an ASCII string representing the
address in . notation. The routine inet_makeaddr(3) takes an
Internet network number and a local network address and constructs
an Internet address from it. The routines inet_netof(3) and inet_lnaof(3)
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.
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 can be decimal, octal, or hexadecimal, as specified in the C language. That is, a leading 0x or 0X implies hexadecimal; otherwise, a leading 0 implies octal; otherwise, the number is interpreted as decimal.
The constant INADDR_NONE is returned by inet_addr(3) and inet_network(3) for malformed requests.
The value INADDR_NONE (0xffffffff) is a valid broadcast address, but inet_addr(3) cannot return that value without indicating failure. The newer inet_aton(3) function does not share this problem. The problem of host byte ordering compared to network byte ordering is confusing. The string returned by inet_ntoa(3) resides in a static memory area.
Inet_addr should return a struct in_addr.