IPv4 Internet host addresses are represented in some contexts as integers
(type uint32_t). In other contexts, the integer is
packaged inside a structure of type struct in_addr. It would
be better if the usage were made consistent, but it is not hard to extract
the integer from the structure or put the integer into a structure.
You will find older code that uses unsigned long int for
IPv4 Internet host addresses instead of uint32_t or struct
in_addr. Historically unsigned long int was a 32-bit number but
with 64-bit machines this has changed. Using unsigned long int
might break the code if it is used on machines where this type doesn't
have 32 bits. uint32_t is specified by Unix98 and guaranteed to have
32 bits.
IPv6 Internet host addresses have 128 bits and are packaged inside a
structure of type struct in6_addr.
The following basic definitions for Internet addresses are declared in the header file `netinet/in.h':
s_addr, which records
the host address number as an uint32_t.
INADDR_LOOPBACK
specially, avoiding any network traffic for the case of one machine
talking to itself.
sin_addr member of struct
sockaddr_in when you want to accept Internet connections.
IN6ADDR_LOOPBACK_INIT is provided to allow you to initialize your
own variables to this value.
IN6ADDR_ANY_INIT is provided to allow you to initialize your
own variables to this value.
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