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Sockets input/output
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<H3 CLASS="subsection"><A NAME="htoc273">7.28</A> Sockets input/output</H3><UL>
<LI><A HREF="gprolog051.html#toc224">Introduction</A>
<LI><A HREF="gprolog051.html#toc225"><TT>socket/2</TT></A>
<LI><A HREF="gprolog051.html#toc226"><TT>socket_close/1</TT></A>
<LI><A HREF="gprolog051.html#toc227"><TT>socket_bind/2</TT></A>
<LI><A HREF="gprolog051.html#toc228"><TT>socket_connect/4</TT></A>
<LI><A HREF="gprolog051.html#toc229"><TT>socket_listen/2</TT></A>
<LI><A HREF="gprolog051.html#toc230"><TT>socket_accept/4</TT>,
<TT>socket_accept/3</TT></A>
<LI><A HREF="gprolog051.html#toc231"><TT>hostname_address/2</TT></A>
</UL>
<A NAME="Sockets-input/output"></A>
<A NAME="toc224"></A>
<H4 CLASS="subsubsection"><A NAME="htoc274">7.28.1</A> Introduction</H4>
<A NAME="Introduction:(Sockets-input/output)"></A>
This set of predicates provides a way to manipulate sockets. The predicates
are straightforward interfaces to the corresponding BSD-type socket
functions. This facility is available if the sockets part of GNU Prolog has
been installed. A reader familiar with BSD sockets will understand them
immediately otherwise a study of sockets is needed. <BR>
<BR>
The domain is either the atom <TT>'AF_INET'</TT> or <TT>'AF_UNIX'</TT>
corresponding to the same domains in BSD-type sockets.<BR>
<BR>
An address is either of the form <TT>'AF_INET'(HostName, Port)</TT> or
<TT>'AF_UNIX'(SocketName)</TT>. <TT>HostName</TT> is an atom denoting a
machine name, <TT>Port</TT> is a port number and <TT>SocketName</TT> is an
atom denoting a socket. <BR>
<BR>
By default, streams associated with sockets are <TT>block</TT> buffered. The
predicate <TT>set_stream_buffering/2</TT> (section <A HREF="gprolog033.html#set-stream-buffering/2">7.10.27</A>)
can be used to change this mode. They are also text streams by default. Use
<TT>set_stream_type/2</TT> (section <A HREF="gprolog033.html#set-stream-type/2">7.10.25</A>) to change the type
if binary streams are needed.<BR>
<BR>
<A NAME="toc225"></A>
<H4 CLASS="subsubsection"><A NAME="htoc275">7.28.2</A> <TT>socket/2</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
socket(+socket_domain, -integer)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>socket(Domain, Socket)</TT> creates a socket whose domain is
<TT>Domain</TT> (section <A HREF="#Sockets-input/output">7.28</A>) and unifies <TT>Socket</TT>
with the descriptor identifying the socket. This predicate is an interface
to the C Unix function <TT>socket(2)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Domain</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Domain</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Domain)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Domain</TT> is an atom but not a valid socket domain</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(socket_domain, Domain)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Socket</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, Socket)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section <A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc226"></A>
<H4 CLASS="subsubsection"><A NAME="htoc276">7.28.3</A> <TT>socket_close/1</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
socket_close(+integer)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>socket_close(Socket)</TT> closes the socket whose descriptor is
<TT>Socket</TT>. This predicate should not be used if <TT>Socket</TT> has
given rise to a stream, e.g. by <TT>socket_connect/4</TT>
(section <A HREF="#socket-connect/4">7.28.5</A>). In that case simply use <TT>close/2</TT>
(section <A HREF="gprolog033.html#close/2">7.10.7</A>) on the associated stream.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Socket</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Socket</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Socket)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section <A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc227"></A>
<H4 CLASS="subsubsection"><A NAME="htoc277">7.28.4</A> <TT>socket_bind/2</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
socket_bind(+integer, +socket_address)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>socket_bind(Socket, Address)</TT> binds the socket whose descriptor is
<TT>Socket</TT> to the address specified by <TT>Address</TT>
(section <A HREF="#Sockets-input/output">7.28</A>). If <TT>Address</TT> if of the form
<TT>'AF_INET'(HostName, Port)</TT> and if <TT>HostName</TT> is
uninstantiated then it is unified with the current machine name. If
<TT>Port</TT> is uninstantiated, it is unified to a port number picked by
the operating system. This predicate is an interface to the C Unix function
<TT>bind(2)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Socket</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Socket</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Socket)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> is neither a variable nor a valid address</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(socket_address, Address)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> = <TT>'AF_UNIX'(E)</TT> and <TT>E</TT> is a
variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> = <TT>'AF_UNIX'(E)</TT> or <TT>'AF_INET'(E,
_)</TT> and <TT>E</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> = <TT>'AF_UNIX'(E)</TT> and <TT>E</TT> is an atom
but not a valid pathname</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_path, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> = <TT>'AF_INET'(_, E)</TT> and <TT>E</TT> is
neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section <A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc228"></A>
<H4 CLASS="subsubsection"><A NAME="htoc278">7.28.5</A> <TT>socket_connect/4</TT></H4>
<A NAME="socket-connect/4"></A>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
socket_connect(+integer, +socket_address, -stream, -stream)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>socket_connect(Socket, Address, StreamIn, StreamOut)</TT> connects the
socket whose descriptor is <TT>Socket</TT> to the address specified by
<TT>Address</TT> (section <A HREF="#Sockets-input/output">7.28</A>). <TT>StreamIn</TT> is
unified with a stream-term associated with the input of the connection (it is
an input stream). Reading from this stream gets data from the socket.
<TT>StreamOut</TT> is unified with a stream-term associated with the output of
the connection (it is an output stream). Writing to this stream sends data
to the socket. The use of <TT>select/5</TT> can be useful
(section <A HREF="gprolog050.html#select/5">7.27.29</A>). This predicate is an interface to the C Unix function
<TT>connect(2)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Socket</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Socket</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Socket)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> is neither a variable nor a valid address</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(socket_address, Address)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> = <TT>'AF_UNIX'(E)</TT> or <TT>'AF_INET'(E,
_)</TT> or <TT>Address</TT> = <TT>'AF_INET'(_, E)</TT> and <TT>E</TT> is a
variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> = <TT>'AF_UNIX'(E)</TT> or <TT>'AF_INET'(E,
_)</TT> and <TT>E</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> = <TT>'AF_UNIX'(E)</TT> and <TT>E</TT> is an atom
but not a valid pathname</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_path, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> = <TT>'AF_INET'(_, E)</TT> and <TT>E</TT> is
neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>StreamIn</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, StreamIn)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>StreamOut</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, StreamOut)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section <A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc229"></A>
<H4 CLASS="subsubsection"><A NAME="htoc279">7.28.6</A> <TT>socket_listen/2</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
socket_listen(+integer, +integer)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>socket_listen(Socket, Length)</TT> defines the socket whose descriptor
is <TT>Socket</TT> to have a maximum backlog queue of <TT>Length</TT>
pending connections. This predicate is an interface to the C Unix function
<TT>listen(2)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Socket</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Socket</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Socket)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Length</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Length</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Length)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section <A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc230"></A>
<H4 CLASS="subsubsection"><A NAME="htoc280">7.28.7</A> <TT>socket_accept/4</TT>,
<TT>socket_accept/3</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
socket_accept(+integer, -atom, -stream, -stream)<BR>
socket_accept(+integer, -stream, -stream)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>socket_accept(Socket, Client, StreamIn, StreamOut)</TT> extracts the
first connection to the socket whose descriptor is <TT>Socket</TT>. If the
domain is <TT>'AF_INET'</TT>, <TT>Client</TT> is unified with an atom whose
name is the Internet host address in numbers-and-dots notation of the
connecting machine. <TT>StreamIn</TT> is unified with a stream-term
associated with the input of the connection (it is an input stream). Reading
from this stream gets data from the socket. <TT>StreamOut</TT> is unified
with a stream-term associated with the output of the connection (it is an
output stream). Writing to this stream sends data to the socket. The use of
<TT>select/5</TT> can be useful (section <A HREF="gprolog050.html#select/5">7.27.29</A>). This predicate is an
interface to the C Unix function <TT>accept(2)</TT>.<BR>
<BR>
<TT>socket_accept(Socket, StreamIn, StreamOut)</TT> is equivalent to
<TT>socket_accept(Socket, _,<BR>
StreamIn, StreamOut)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Socket</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Socket</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Socket)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Client</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, Client)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>StreamIn</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, StreamIn)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>StreamOut</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, StreamOut)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section <A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicates.<BR>
<BR>
<A NAME="toc231"></A>
<H4 CLASS="subsubsection"><A NAME="htoc281">7.28.8</A> <TT>hostname_address/2</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
hostname_address(+atom, ?atom)<BR>
hostname_address(?atom, +atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>hostname_address(HostName, HostAddress)</TT> succeeds if the Internet
host address in numbers-and-dots notation of <TT>HostName</TT> is
<TT>HostAddress</TT>. <TT>Hostname</TT> can be given as a fully qualified
name, or an unqualified name or an alias of the machine. The predicate will
fail if the machine name or address cannot be resolved.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>HostName</TT> and <TT>HostAddress</TT> are variables</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>HostName</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, HostName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>HostAddress</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, HostAddress)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Address</TT> is neither a variable nor a valid address</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(socket_address, Address)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
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Copyright (C) 1999-2007 Daniel Diaz
<BR>
<BR>
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