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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title><netdb.h></title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="<netdb.h>"></a> <a name="tag_13_31"></a><!-- <netdb.h> --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_13_31_01"></a>NAME</h4><blockquote>netdb.h - definitions for network database operations</blockquote><h4><a name="tag_13_31_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><tt>#include <netdb.h></tt></p></blockquote><h4><a name="tag_13_31_03"></a>DESCRIPTION</h4><blockquote><p>The <i><netdb.h></i> header may define the <b>in_port_t</b> type and the <b>in_addr_t</b> type as described in <a href="netinet/in.h.html"><i><netinet/in.h></i></a> .</p><p>The <i><netdb.h></i> header shall define the <b>hostent</b> structure that includes at least the following members:</p><pre><tt>char *h_name </tt> Official name of the host. <tt>char **h_aliases </tt> A pointer to an array of pointers to <tt> </tt> alternative host names, terminated by a <tt> </tt> null pointer. <tt>int h_addrtype </tt> Address type. <tt>int h_length </tt> The length, in bytes, of the address. <tt>char **h_addr_list </tt> A pointer to an array of pointers to network <tt> </tt> addresses (in network byte order) for the host, <tt> </tt> terminated by a null pointer. <tt></tt></pre><p>The <i><netdb.h></i> header shall define the <b>netent</b> structure that includes at least the following members:</p><pre><tt>char *n_name </tt> Official, fully-qualified (including the <tt> </tt> domain) name of the host. <tt>char **n_aliases </tt> A pointer to an array of pointers to <tt> </tt> alternative network names, terminated by a <tt> </tt> null pointer. <tt>int n_addrtype </tt> The address type of the network. <tt>uint32_t n_net </tt> The network number, in host byte order. <tt></tt></pre><p>The <b>uint32_t</b> type shall be defined as described in <a href="inttypes.h.html"><i><inttypes.h></i></a> .</p><p>The <i><netdb.h></i> header shall define the <b>protoent</b> structure that includes at least the following members:</p><pre><tt>char *p_name </tt> Official name of the protocol. <tt>char **p_aliases </tt> A pointer to an array of pointers to <tt> </tt> alternative protocol names, terminated by <tt> </tt> a null pointer. <tt>int p_proto </tt> The protocol number. <tt></tt></pre><p>The <i><netdb.h></i> header shall define the <b>servent</b> structure that includes at least the following members:</p><pre><tt>char *s_name </tt> Official name of the service. <tt>char **s_aliases </tt> A pointer to an array of pointers to <tt> </tt> alternative service names, terminated by <tt> </tt> a null pointer. <tt>int s_port </tt> The port number at which the service <tt> </tt> resides, in network byte order. <tt>char *s_proto </tt> The name of the protocol to use when <tt> </tt> contacting the service. <tt></tt></pre><p>The <i><netdb.h></i> header shall define the IPPORT_RESERVED macro with the value of the highest reserved Internet portnumber.</p><p><sup>[<a href="javascript:open_code('OB')">OB</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">When the <i><netdb.h></i> header is included, <i>h_errno</i> shall be available as a modifiable lvalue of type <b>int</b>. Itis unspecified whether <i>h_errno</i> is a macro or an identifier declared with external linkage. <img src="../images/opt-end.gif"alt="[Option End]" border="0"></p><p>The <i><netdb.h></i> header shall define the following macros for use as error values for <a href="../functions/gethostbyaddr.html"><i>gethostbyaddr</i>()</a> and <a href="../functions/gethostbyname.html"><i>gethostbyname</i>()</a>:</p><blockquote><pre>HOST_NOT_FOUNDNO_DATANO_RECOVERYTRY_AGAIN</pre></blockquote><h5><a name="tag_13_31_03_01"></a>Address Information Structure</h5><p>The <i><netdb.h></i> header shall define the <b>addrinfo</b> structure that includes at least the following members:</p><pre><tt>int ai_flags </tt> Input flags. <tt>int ai_family </tt> Address family of socket. <tt>int ai_socktype </tt> Socket type. <tt>int ai_protocol </tt> Protocol of socket. <tt>socklen_t ai_addrlen </tt> Length of socket address. <tt>struct sockaddr *ai_addr </tt> Socket address of socket. <tt>char *ai_canonname </tt> Canonical name of service location. <tt>struct addrinfo *ai_next </tt> Pointer to next in list. <tt></tt></pre><p>The <i><netdb.h></i> header shall define the following macros that evaluate to bitwise-distinct integer constants for usein the <i>flags</i> field of the <b>addrinfo</b> structure:</p><dl compact><dt>AI_PASSIVE</dt><dd>Socket address is intended for <a href="../functions/bind.html"><i>bind</i>()</a>.</dd><dt>AI_CANONNAME</dt><dd><br>Request for canonical name.</dd><dt>AI_NUMERICHOST</dt><dd><br>Return numeric host address as name.</dd><dt>AI_NUMERICSERV</dt><dd><br>Inhibit service name resolution.</dd><dt>AI_V4MAPPED</dt><dd>If no IPv6 addresses are found, query for IPv4 addresses and return them to the caller as IPv4-mapped IPv6 addresses.</dd><dt>AI_ALL</dt><dd>Query for both IPv4 and IPv6 addresses.</dd><dt>AI_ADDRCONFIG</dt><dd><br>Query for IPv4 addresses only when an IPv4 address is configured; query for IPv6 addresses only when an IPv6 address isconfigured.</dd></dl><p>The <i><netdb.h></i> header shall define the following macros that evaluate to bitwise-distinct integer constants for usein the <i>flags</i> argument to <a href="../functions/getnameinfo.html"><i>getnameinfo</i>()</a>:</p><dl compact><dt>NI_NOFQDN</dt><dd>Only the nodename portion of the FQDN is returned for local hosts.</dd><dt>NI_NUMERICHOST</dt><dd><br>The numeric form of the node's address is returned instead of its name.</dd><dt>NI_NAMEREQD</dt><dd>Return an error if the node's name cannot be located in the database.</dd><dt>NI_NUMERICSERV</dt><dd><br>The numeric form of the service address is returned instead of its name.</dd><dt>NI_NUMERICSCOPE</dt><dd><br>For IPv6 addresses, the numeric form of the scope identifier is returned instead of its name.</dd><dt>NI_DGRAM</dt><dd>Indicates that the service is a datagram service (SOCK_DGRAM).</dd></dl><h5><a name="tag_13_31_03_02"></a>Address Information Errors</h5><p>The <i><netdb.h></i> header shall define the following macros for use as error values for <a href="../functions/getaddrinfo.html"><i>getaddrinfo</i>()</a> and <a href="../functions/getnameinfo.html"><i>getnameinfo</i>()</a>:</p><dl compact><dt>EAI_AGAIN</dt><dd>The name could not be resolved at this time. Future attempts may succeed.</dd><dt>EAI_BADFLAGS</dt><dd>The flags had an invalid value.</dd><dt>EAI_FAIL</dt><dd>A non-recoverable error occurred.</dd><dt>EAI_FAMILY</dt><dd>The address family was not recognized or the address length was invalid for the specified family.</dd><dt>EAI_MEMORY</dt><dd>There was a memory allocation failure.</dd><dt>EAI_NONAME</dt><dd>The name does not resolve for the supplied parameters. <p>NI_NAMEREQD is set and the host's name cannot be located, or both <i>nodename</i> and <i>servname</i> were null.</p></dd><dt>EAI_SERVICE</dt><dd>The service passed was not recognized for the specified socket type.</dd><dt>EAI_SOCKTYPE</dt><dd>The intended socket type was not recognized.</dd><dt>EAI_SYSTEM</dt><dd>A system error occurred. The error code can be found in <i>errno</i>.</dd><dt>EAI_OVERFLOW</dt><dd><br>An argument buffer overflowed.</dd></dl><p>The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.</p><pre><tt>void endhostent(void);void endnetent(void);void endprotoent(void);void endservent(void);void freeaddrinfo(struct addrinfo *);const char *gai_strerror(int);int getaddrinfo(const char *restrict, const char *restrict, const struct addrinfo *restrict, struct addrinfo **restrict);struct hostent *gethostbyaddr(const void *, socklen_t, int);struct hostent *gethostbyname(const char *);struct hostent *gethostent(void);int getnameinfo(const struct sockaddr *restrict, socklen_t, char *restrict, socklen_t, char *restrict, socklen_t, int);struct netent *getnetbyaddr(uint32_t, int);struct netent *getnetbyname(const char *);struct netent *getnetent(void);struct protoent *getprotobyname(const char *);struct protoent *getprotobynumber(int);struct protoent *getprotoent(void);struct servent *getservbyname(const char *, const char *);struct servent *getservbyport(int, const char *);struct servent *getservent(void);void sethostent(int);void setnetent(int);void setprotoent(int);void setservent(int);</tt></pre><p>The type <b>socklen_t</b> shall be defined through <b>typedef</b> as described in <a href="../basedefs/sys/socket.h.html"><i><sys/socket.h></i></a>.</p><p>Inclusion of the <i><netdb.h></i> header may also make visible all symbols from <a href="../basedefs/netinet/in.h.html"><i><netinet/in.h></i></a>, <a href="../basedefs/sys/socket.h.html"><i><sys/socket.h></i></a>, and <a href="../basedefs/inttypes.h.html"><i><inttypes.h></i></a>.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_13_31_04"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_13_31_05"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_13_31_06"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_13_31_07"></a>SEE ALSO</h4><blockquote><p><a href="netinet/in.h.html"><i><netinet/in.h></i></a> , <a href="inttypes.h.html"><i><inttypes.h></i></a> , <a href="sys/socket.h.html"><i><sys/socket.h></i></a> , the System Interfaces volume of IEEE Std 1003.1-2001, <a href="../functions/bind.html"><i>bind</i>()</a>, <a href="../functions/endhostent.html"><i>endhostent</i>()</a>, <a href="../functions/endnetent.html"><i>endnetent</i>()</a>, <a href="../functions/endprotoent.html"><i>endprotoent</i>()</a>, <a href="../functions/endservent.html"><i>endservent</i>()</a>, <a href="../functions/getaddrinfo.html"><i>getaddrinfo</i>()</a>, <a href="../functions/getnameinfo.html"><i>getnameinfo</i>()</a></p></blockquote><h4><a name="tag_13_31_08"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 6. Derived from the XNS, Issue 5.2 specification.</p><p>The Open Group Base Resolution bwg2001-009 is applied, which changes the return type for <a href="../functions/gai_strerror.html"><i>gai_strerror</i>()</a> from <b>char *</b> to <b>const char *</b>. This is for coordination withthe IPnG Working Group.</p><p>IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/11 is applied, adding a description of the NI_NUMERICSCOPE macro andcorrecting the <a href="../functions/getnameinfo.html"><i>getnameinfo</i>()</a> function prototype. These changes are for alignmentwith IPv6.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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