/usr/lib/swi-prolog/doc/Manual/readutil.html

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<h2 id="sec:readutil"><a id="sec:A.25"><span class="sec-nr">A.25</span> <span class="sec-title">library(readutil): 
Reading lines, streams and files</span></a></h2>

<a id="sec:readutil"></a>

<p>This library contains primitives to read lines, files, multiple 
terms, etc. The package <code>clib</code> provides a shared object (DLL) 
named <code>readutil</code>. If the library can locate this shared 
object it will use the foreign implementation for reading character 
codes. Otherwise it will use a Prolog implementation. Distributed 
applications should make sure to deliver the <code>readutil</code> 
shared object if performance of these predicates is critical.

<dl class="latex">
<dt class="pubdef"><a id="read_line_to_codes/2"><strong>read_line_to_codes</strong>(<var>+Stream, 
-Codes</var>)</a></dt>
<dd class="defbody">
Read the next line of input from <var>Stream</var> and unify the result 
with
<var>Codes</var> <em>after</em> the line has been read. A line is ended 
by a newline character or end-of-file. Unlike <a id="idx:readlinetocodes3:1818"></a><a class="pred" href="readutil.html#read_line_to_codes/3">read_line_to_codes/3</a>, 
this predicate removes a trailing newline character.

<p>On end-of-file the atom <code>end_of_file</code> is returned. See 
also
<a id="idx:atendofstream01:1819"></a><span class="pred-ext">at_end_of_stream/[0,1]</span>.</dd>
<dt class="pubdef"><a id="read_line_to_codes/3"><strong>read_line_to_codes</strong>(<var>+Stream, 
-Codes, ?Tail</var>)</a></dt>
<dd class="defbody">
Difference-list version to read an input line to a list of character 
codes. Reading stops at the newline or end-of-file character, but unlike <a id="idx:readlinetocodes2:1820"></a><a class="pred" href="readutil.html#read_line_to_codes/2">read_line_to_codes/2</a>, 
the newline is retained in the output. This predicate is especially 
useful for reading a block of lines up to some delimiter. The following 
example reads an HTTP header ended by a blank line:

<pre class="code">
read_header_data(Stream, Header) :-
        read_line_to_codes(Stream, Header, Tail),
        read_header_data(Header, Stream, Tail).

read_header_data("\r\n", _, _) :- !.
read_header_data("\n", _, _) :- !.
read_header_data("", _, _) :- !.
read_header_data(_, Stream, Tail) :-
        read_line_to_codes(Stream, Tail, NewTail),
        read_header_data(Tail, Stream, NewTail).
</pre>

</dd>
<dt class="pubdef"><a id="read_stream_to_codes/2"><strong>read_stream_to_codes</strong>(<var>+Stream, 
-Codes</var>)</a></dt>
<dd class="defbody">
Read all input until end-of-file and unify the result to <var>Codes</var>.</dd>
<dt class="pubdef"><a id="read_stream_to_codes/3"><strong>read_stream_to_codes</strong>(<var>+Stream, 
-Codes, ?Tail</var>)</a></dt>
<dd class="defbody">
Difference-list version of <a id="idx:readstreamtocodes2:1821"></a><a class="pred" href="readutil.html#read_stream_to_codes/2">read_stream_to_codes/2</a>.</dd>
<dt class="pubdef"><a id="read_file_to_codes/3"><strong>read_file_to_codes</strong>(<var>+Spec, 
-Codes, +Options</var>)</a></dt>
<dd class="defbody">
Read a file to a list of character codes. <var>Spec</var> is a file 
specification for <a id="idx:absolutefilename3:1822"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>. <var>Codes</var> 
is the resulting code list. <var>Options</var> is a list of options for
<a id="idx:absolutefilename3:1823"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a> 
and <a id="idx:open4:1824"></a><a class="pred" href="IO.html#open/4">open/4</a>. 
In addition, the option
<code>tail(Tail)</code> is defined, forming a difference-list.</dd>
<dt class="pubdef"><a id="read_file_to_terms/3"><strong>read_file_to_terms</strong>(<var>+Spec, 
-Terms, +Options</var>)</a></dt>
<dd class="defbody">
Read a file to a list of Prolog terms (see <a id="idx:read1:1825"></a><a class="pred" href="termrw.html#read/1">read/1</a>). <var>Spec</var> 
is a file specification for <a id="idx:absolutefilename3:1826"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>. <var>Terms</var> 
is the resulting list of Prolog terms. <var>Options</var> is a list of 
options for
<a id="idx:absolutefilename3:1827"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a> 
and <a id="idx:open4:1828"></a><a class="pred" href="IO.html#open/4">open/4</a>. 
In addition, the option
<code>tail(Tail)</code> is defined, forming a difference-list.
</dd>
</dl>

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swi-prolog-nox 6.6.4-2ubuntu1 / usr / lib / swi-prolog / doc / Manual / readutil.html
