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(libc.info)Internet Address Formats

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Internet Socket Address Formats
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   In the Internet namespace, for both IPv4 (`AF_INET') and IPv6
(`AF_INET6'), a socket address consists of a host address and a port on
that host.  In addition, the protocol you choose serves effectively as
a part of the address because local port numbers are meaningful only
within a particular protocol.

   The data types for representing socket addresses in the Internet
namespace are defined in the header file `netinet/in.h'.

 - Data Type: struct sockaddr_in
     This is the data type used to represent socket addresses in the
     Internet namespace.  It has the following members:

    `sa_family_t sin_family'
          This identifies the address family or format of the socket
          address.  You should store the value `AF_INET' in this member.
          Note: Socket Addresses.

    `struct in_addr sin_addr'
          This is the Internet address of the host machine.  Note: Host
          Addresses, and Note: Host Names, for how to get a value
          to store here.

    `unsigned short int sin_port'
          This is the port number.  Note: Ports.

   When you call `bind' or `getsockname', you should specify `sizeof
(struct sockaddr_in)' as the LENGTH parameter if you are using an IPv4
Internet namespace socket address.

 - Data Type: struct sockaddr_in6
     This is the data type used to represent socket addresses in the
     IPv6 namespace.  It has the following members:

    `sa_family_t sin6_family'
          This identifies the address family or format of the socket
          address.  You should store the value of `AF_INET6' in this
          member.  Note: Socket Addresses.

    `struct in6_addr sin6_addr'
          This is the IPv6 address of the host machine.  Note: Host
          Addresses, and Note: Host Names, for how to get a value
          to store here.

    `uint32_t sin6_flowinfo'
          This is a currently unimplemented field.

    `uint16_t sin6_port'
          This is the port number.  Note: Ports.