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| <h5 class="subsubsection">16.6.2.2 Host Address Data Type</h5> |
| |
| <p>IPv4 Internet host addresses are represented in some contexts as integers |
| (type <code>uint32_t</code>). In other contexts, the integer is |
| packaged inside a structure of type <code>struct in_addr</code>. 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. |
| |
| <p>You will find older code that uses <code>unsigned long int</code> for |
| IPv4 Internet host addresses instead of <code>uint32_t</code> or <code>struct |
| in_addr</code>. Historically <code>unsigned long int</code> was a 32-bit number but |
| with 64-bit machines this has changed. Using <code>unsigned long int</code> |
| might break the code if it is used on machines where this type doesn't |
| have 32 bits. <code>uint32_t</code> is specified by Unix98 and guaranteed to have |
| 32 bits. |
| |
| <p>IPv6 Internet host addresses have 128 bits and are packaged inside a |
| structure of type <code>struct in6_addr</code>. |
| |
| <p>The following basic definitions for Internet addresses are declared in |
| the header file <samp><span class="file">netinet/in.h</span></samp>: |
| <a name="index-netinet_002fin_002eh-1693"></a> |
| <!-- netinet/in.h --> |
| <!-- BSD --> |
| |
| <div class="defun"> |
| — Data Type: <b>struct in_addr</b><var><a name="index-struct-in_005faddr-1694"></a></var><br> |
| <blockquote><p>This data type is used in certain contexts to contain an IPv4 Internet |
| host address. It has just one field, named <code>s_addr</code>, which records |
| the host address number as an <code>uint32_t</code>. |
| </p></blockquote></div> |
| |
| <!-- netinet/in.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: uint32_t <b>INADDR_LOOPBACK</b><var><a name="index-INADDR_005fLOOPBACK-1695"></a></var><br> |
| <blockquote><p>You can use this constant to stand for “the address of this machine,” |
| instead of finding its actual address. It is the IPv4 Internet address |
| ‘<samp><span class="samp">127.0.0.1</span></samp>’, which is usually called ‘<samp><span class="samp">localhost</span></samp>’. This |
| special constant saves you the trouble of looking up the address of your |
| own machine. Also, the system usually implements <code>INADDR_LOOPBACK</code> |
| specially, avoiding any network traffic for the case of one machine |
| talking to itself. |
| </p></blockquote></div> |
| |
| <!-- netinet/in.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: uint32_t <b>INADDR_ANY</b><var><a name="index-INADDR_005fANY-1696"></a></var><br> |
| <blockquote><p>You can use this constant to stand for “any incoming address” when |
| binding to an address. See <a href="Setting-Address.html#Setting-Address">Setting Address</a>. This is the usual |
| address to give in the <code>sin_addr</code> member of <code>struct sockaddr_in</code><!-- /@w --> when you want to accept Internet connections. |
| </p></blockquote></div> |
| |
| <!-- netinet/in.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: uint32_t <b>INADDR_BROADCAST</b><var><a name="index-INADDR_005fBROADCAST-1697"></a></var><br> |
| <blockquote><p>This constant is the address you use to send a broadcast message. |
| <!-- !!! broadcast needs further documented --> |
| </p></blockquote></div> |
| |
| <!-- netinet/in.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: uint32_t <b>INADDR_NONE</b><var><a name="index-INADDR_005fNONE-1698"></a></var><br> |
| <blockquote><p>This constant is returned by some functions to indicate an error. |
| </p></blockquote></div> |
| |
| <!-- netinet/in.h --> |
| <!-- IPv6 basic API --> |
| <div class="defun"> |
| — Data Type: <b>struct in6_addr</b><var><a name="index-struct-in6_005faddr-1699"></a></var><br> |
| <blockquote><p>This data type is used to store an IPv6 address. It stores 128 bits of |
| data, which can be accessed (via a union) in a variety of ways. |
| </p></blockquote></div> |
| |
| <!-- netinet/in.h --> |
| <!-- IPv6 basic API --> |
| <div class="defun"> |
| — Constant: struct in6_addr <b>in6addr_loopback</b><var><a name="index-in6addr_005floopback-1700"></a></var><br> |
| <blockquote><p>This constant is the IPv6 address ‘<samp><span class="samp">::1</span></samp>’, the loopback address. See |
| above for a description of what this means. The macro |
| <code>IN6ADDR_LOOPBACK_INIT</code> is provided to allow you to initialize your |
| own variables to this value. |
| </p></blockquote></div> |
| |
| <!-- netinet/in.h --> |
| <!-- IPv6 basic API --> |
| <div class="defun"> |
| — Constant: struct in6_addr <b>in6addr_any</b><var><a name="index-in6addr_005fany-1701"></a></var><br> |
| <blockquote><p>This constant is the IPv6 address ‘<samp><span class="samp">::</span></samp>’, the unspecified address. See |
| above for a description of what this means. The macro |
| <code>IN6ADDR_ANY_INIT</code> is provided to allow you to initialize your |
| own variables to this value. |
| </p></blockquote></div> |
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