perlhacktut.html 30.6 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
  <title>perlhacktut - perldoc.perl.org</title>
  <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
  <meta http-equiv="Content-Language" content="en-gb">
  <link rel="search" type="application/opensearchdescription+xml" title="Search perldoc.perl.org" href="/static/search.xml"/>
  <link href="static/css-20100830.css" rel="stylesheet" rev="stylesheet" type="text/css" media="screen">
  <link href="static/exploreperl.css" rel="stylesheet" rev="stylesheet" type="text/css">
</head>

<body onLoad="perldoc.startup();" onPageShow="if (event.persisted) perldoc.startup();">
    <div id="page">
      
      <div id="header">
	<div id="homepage_link">
	  <a href="index.html"></a>
	</div>
	<div id="strapline">
	  Perl Programming Documentation
	</div>
	<div id="download_link" class="download">
	  <a href="http://www.perl.org/get.html">Download Perl</a>
	</div>
	<div id="explore_link" class="download">
	  <a id="explore_anchor" href="#">Explore</a>
	</div>
      </div>
      
      <div id="body">
        <div id="left_column">
          <div class="side_group">
            
	    <div class="side_panel doc_panel">
              <p>Manual</p>
              <ul>
                <li><a href="index-overview.html">Overview</a>
                <li><a href="index-tutorials.html">Tutorials</a>
                <li><a href="index-faq.html">FAQs</a>
                <li><a href="index-history.html">History / Changes</a>
                <li><a href="index-licence.html">License</a>
              </ul>
            </div>
            <div class="side_panel doc_panel">
              <p>Reference</p>
              <ul>
                <li><a href="index-language.html">Language</a>
                <li><a href="index-functions.html">Functions</a>
                <li><a href="perlop.html">Operators</a>
                <li><a href="perlvar.html">Special Variables</a>
                <li><a href="index-pragmas.html">Pragmas</a>
                <li><a href="index-utilities.html">Utilities</a>
                <li><a href="index-internals.html">Internals</a>
                <li><a href="index-platforms.html">Platform Specific</a>
              </ul>
            </div>
            <div class="side_panel doc_panel">
              <p>Modules</p>
              <ul>
		<li>
		
                
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		
                  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		
                  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		
                  
		
                  
		    
		  
		
                  
		
                  
		
		
                    <a href="index-modules-A.html">A</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-B.html">B</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-C.html">C</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-D.html">D</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-E.html">E</a>
                    
                      
                        <li>
                      
                    
                
                    <a href="index-modules-F.html">F</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-G.html">G</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-H.html">H</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-I.html">I</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-L.html">L</a>
                    
                      
                        <li>
                      
                    
                
                    <a href="index-modules-M.html">M</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-N.html">N</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-O.html">O</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-P.html">P</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-S.html">S</a>
                    
                      
                        <li>
                      
                    
                
                    <a href="index-modules-T.html">T</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-U.html">U</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-X.html">X</a>
                    
                
              </ul>
            </div>
            
	      <div class="side_panel doc_panel">
		<p>Tools</p>
		<ul>
		  <li><a href="preferences.html">Preferences</a>
		</ul>
	      </div>
            
          </div>
        </div>
        <div id="centre_column">
          <div id="content_header">
            <div id="title_bar">
              <div id="page_name">
                <h1>perlhacktut</h1>
              </div>
              <div id="perl_version">
294
                Perl 5 version 26.0 documentation
295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429
              </div>
              <div class="page_links" id="page_links_top">
                <a href="#" onClick="toolbar.goToTop();return false;">Go to top</a>
		
              </div>
	      <div class="page_links" id="page_links_bottom">
		
                  <a href="#" id="page_index_toggle">Show page index</a> &bull;
		
                <a href="#" id="recent_pages_toggle">Show recent pages</a>		
	      </div>
	      <div id="search_form">
		<form action="search.html" method="GET" id="search">
		  <input type="text" name="q" id="search_box" alt="Search">
		</form>
	      </div>
            </div>
            <div id="breadcrumbs">
                
    <a href="index.html">Home</a> &gt;
    
      
        <a href="index-internals.html">Internals and C language interface</a> &gt;
      
    
    perlhacktut
  

            </div>
          </div>
          <div id="content_body">
	    <!--[if lt IE 7]>
 <div class="noscript">
   <p>
     <strong>It looks like you're using Internet Explorer 6. This is a very old
     browser which does not offer full support for modern websites.</strong>
   </p>
   <p>
     Unfortunately this means that this website will not work on
     your computer.
   </p>
   <p>
     Don't miss out though! To view the site (and get a better experience from
     many other websites), simply upgrade to
     <a href="http://www.microsoft.com/windows/Internet-explorer/default.aspx">Internet
Explorer 8</a>
     or download an alternative browser such as
     <a href="http://www.mozilla.com/en-US/firefox/firefox.html">Firefox</a>,
     <a href="http://www.apple.com/safari/download/">Safari</a>, or
     <a href="http://www.google.co.uk/chrome">Google Chrome</a>.
   </p>
   <p>
     All of these browsers are free. If you're using a PC at work, you may
     need to contact your IT administrator.
   </p>
 </div>
<![endif]-->
	    <noscript>
	      <div class="noscript">
	      <p>
                <strong>Please note: Many features of this site require JavaScript. You appear to have JavaScript disabled,
	        or are running a non-JavaScript capable web browser.</strong>
	      </p>
	      <p>
		To get the best experience, please enable JavaScript or download a modern web browser such as <a href="http://www.microsoft.com/windows/Internet-explorer/default.aspx">Internet Explorer 8</a>, <a href="http://www.mozilla.com/en-US/firefox/firefox.html">Firefox</a>, <a href="http://www.apple.com/safari/download/">Safari</a>, or <a href="http://www.google.co.uk/chrome">Google Chrome</a>.
              </p>
	      </div>
	    </noscript>

	    <div id="recent_pages" class="hud_container">
	      <div id="recent_pages_header" class="hud_header">
		<div id="recent_pages_close" class="hud_close"><a href="#" onClick="recentPages.hide();return false;"></a></div>
		<div id="recent_pages_title" class="hud_title"><span class="hud_span_top">Recently read</span></div>
		<div id="recent_pages_topright" class="hud_topright"></div>
	      </div>
	      <div id="recent_pages_content" class="hud_content">
	      </div>
	      <div id="recent_pages_footer" class="hud_footer">
		<div id="recent_pages_bottomleft" class="hud_bottomleft"></div>
		<div id="recent_pages_bottom" class="hud_bottom"><span class="hud_span_bottom"></span></div>
		<div id="recent_pages_resize" class="hud_resize"></div>
	      </div>
	    </div>
  
	    <div id="from_search"></div>
            <h1>perlhacktut</h1>


  <!--    -->
<ul><li><a href="#NAME">NAME</a><li><a href="#DESCRIPTION">DESCRIPTION</a><li><a href="#EXAMPLE-OF-A-SIMPLE-PATCH">EXAMPLE OF A SIMPLE PATCH</a><ul><li><a href="#Writing-the-patch">Writing the patch</a><li><a href="#Testing-the-patch">Testing the patch</a><li><a href="#Documenting-the-patch">Documenting the patch</a><li><a href="#Submit">Submit</a></ul><li><a href="#AUTHOR">AUTHOR</a></ul><a name="NAME"></a><h1>NAME</h1>
<p>perlhacktut - Walk through the creation of a simple C code patch</p>
<a name="DESCRIPTION"></a><h1>DESCRIPTION</h1>
<p>This document takes you through a simple patch example.</p>
<p>If you haven't read <a href="perlhack.html">perlhack</a> yet, go do that first! You might also
want to read through <a href="perlsource.html">perlsource</a> too.</p>
<p>Once you're done here, check out <a href="perlhacktips.html">perlhacktips</a> next.</p>
<a name="EXAMPLE-OF-A-SIMPLE-PATCH"></a><h1>EXAMPLE OF A SIMPLE PATCH</h1>
<p>Let's take a simple patch from start to finish.</p>
<p>Here's something Larry suggested: if a <code class="inline"><span class="w">U</span></code>
 is the first active format
during a <code class="inline"><a class="l_k" href="functions/pack.html">pack</a></code>, (for example, <code class="inline"><a class="l_k" href="functions/pack.html">pack</a> <span class="q">&quot;U3C8&quot;</span><span class="cm">,</span> <span class="i">@stuff</span></code>
) then the
resulting string should be treated as UTF-8 encoded.</p>
<p>If you are working with a git clone of the Perl repository, you will
want to create a branch for your changes. This will make creating a
proper patch much simpler. See the <a href="perlgit.html">perlgit</a> for details on how to do
this.</p>
<a name="Writing-the-patch"></a><h2>Writing the patch</h2>
<p>How do we prepare to fix this up? First we locate the code in question
- the <code class="inline"><a class="l_k" href="functions/pack.html">pack</a></code> happens at runtime, so it's going to be in one of the
<i>pp</i> files. Sure enough, <code class="inline"><span class="w">pp_pack</span></code>
 is in <i>pp.c</i>. Since we're going
to be altering this file, let's copy it to <i>pp.c~</i>.</p>
<p>[Well, it was in <i>pp.c</i> when this tutorial was written. It has now
been split off with <code class="inline"><span class="w">pp_unpack</span></code>
 to its own file, <i>pp_pack.c</i>]</p>
<p>Now let's look over <code class="inline"><span class="w">pp_pack</span></code>
: we take a pattern into <code class="inline"><span class="w">pat</span></code>
, and then
loop over the pattern, taking each format character in turn into
<code class="inline"><span class="w">datum_type</span></code>
. Then for each possible format character, we swallow up
the other arguments in the pattern (a field width, an asterisk, and so
on) and convert the next chunk input into the specified format, adding
it onto the output SV <code class="inline"><span class="w">cat</span></code>
.</p>
<p>How do we know if the <code class="inline"><span class="w">U</span></code>
 is the first format in the <code class="inline"><span class="w">pat</span></code>
? Well, if
we have a pointer to the start of <code class="inline"><span class="w">pat</span></code>
 then, if we see a <code class="inline"><span class="w">U</span></code>
 we can
test whether we're still at the start of the string. So, here's where
<code class="inline"><span class="w">pat</span></code>
 is set up:</p>
430 431
<pre class="verbatim"><ol><li>    <span class="w">STRLEN</span> <span class="w">fromlen</span><span class="sc">;</span></li><li>    <span class="w">char</span> *<span class="w">pat</span> = <span class="i">SvPVx</span><span class="s">(</span><span class="i">*+</span>+<span class="w">MARK</span><span class="cm">,</span> <span class="w">fromlen</span><span class="s">)</span><span class="sc">;</span></li><li>    <span class="w">char</span> *<span class="w">patend</span> = <span class="w">pat</span> + <span class="w">fromlen</span><span class="sc">;</span></li><li>    <span class="w">I32</span> <span class="w">len</span><span class="sc">;</span></li><li>    <span class="w">I32</span> <span class="w">datumtype</span><span class="sc">;</span></li><li>    <span class="w">SV</span> *<span class="w">fromstr</span><span class="sc">;</span></li></ol></pre><p>We'll have another string pointer in there:</p>
<pre class="verbatim"><ol><li>    <span class="w">STRLEN</span> <span class="w">fromlen</span><span class="sc">;</span></li><li>    <span class="w">char</span> *<span class="w">pat</span> = <span class="i">SvPVx</span><span class="s">(</span><span class="i">*+</span>+<span class="w">MARK</span><span class="cm">,</span> <span class="w">fromlen</span><span class="s">)</span><span class="sc">;</span></li><li>    <span class="w">char</span> *<span class="w">patend</span> = <span class="w">pat</span> + <span class="w">fromlen</span><span class="sc">;</span></li><li> +  <span class="w">char</span> *<span class="w">patcopy</span><span class="sc">;</span></li><li>    <span class="w">I32</span> <span class="w">len</span><span class="sc">;</span></li><li>    <span class="w">I32</span> <span class="w">datumtype</span><span class="sc">;</span></li><li>    <span class="w">SV</span> *<span class="w">fromstr</span><span class="sc">;</span></li></ol></pre><p>And just before we start the loop, we'll set <code class="inline"><span class="w">patcopy</span></code>
432 433 434
 to be the start
of <code class="inline"><span class="w">pat</span></code>
:</p>
435
<pre class="verbatim"><ol><li>    <span class="w">items</span> = <span class="w">SP</span> - <span class="w">MARK</span><span class="sc">;</span></li><li>    <span class="w">MARK</span>++<span class="sc">;</span></li><li>    <span class="i">SvPVCLEAR</span><span class="s">(</span><span class="w">cat</span><span class="s">)</span><span class="sc">;</span></li><li> +  <span class="w">patcopy</span> = <span class="w">pat</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/while.html">while</a> <span class="s">(</span><span class="w">pat</span> &lt; <span class="w">patend</span><span class="s">)</span> <span class="s">{</span></li></ol></pre><p>Now if we see a <code class="inline"><span class="w">U</span></code>
436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528
 which was at the start of the string, we turn on
the <code class="inline"><span class="w">UTF8</span></code>
 flag for the output SV, <code class="inline"><span class="w">cat</span></code>
:</p>
<pre class="verbatim"><ol><li> +  if (datumtype == 'U' &amp;&amp; pat==patcopy+1)</li><li> +      SvUTF8_on(cat);</li><li>    if (datumtype == '#') {</li><li>        while (pat &lt; patend &amp;&amp; *pat != '\n')</li><li>            pat++;</li></ol></pre><p>Remember that it has to be <code class="inline"><span class="w">patcopy</span>+<span class="n">1</span></code>
 because the first character of
the string is the <code class="inline"><span class="w">U</span></code>
 which has been swallowed into <code class="inline"><span class="w">datumtype</span>!</code>
</p>
<p>Oops, we forgot one thing: what if there are spaces at the start of the
pattern? <code class="inline"><a class="l_k" href="functions/pack.html">pack</a><span class="s">(</span><span class="q">&quot;  U*&quot;</span><span class="cm">,</span> <span class="i">@stuff</span><span class="s">)</span></code>
 will have <code class="inline"><span class="w">U</span></code>
 as the first active
character, even though it's not the first thing in the pattern. In this
case, we have to advance <code class="inline"><span class="w">patcopy</span></code>
 along with <code class="inline"><span class="w">pat</span></code>
 when we see
spaces:</p>
<pre class="verbatim"><ol><li>    if (isSPACE(datumtype))</li><li>        continue;</li></ol></pre><p>needs to become</p>
<pre class="verbatim"><ol><li>    if <span class="s">(</span><span class="i">isSPACE</span><span class="s">(</span><span class="w">datumtype</span><span class="s">)</span><span class="s">)</span> <span class="s">{</span></li><li>        <span class="w">patcopy</span>++<span class="sc">;</span></li><li>        <a class="l_k" href="functions/continue.html">continue</a><span class="sc">;</span></li><li>    <span class="s">}</span></li></ol></pre><p>OK. That's the C part done. Now we must do two additional things before
this patch is ready to go: we've changed the behaviour of Perl, and so
we must document that change. We must also provide some more regression
tests to make sure our patch works and doesn't create a bug somewhere
else along the line.</p>
<a name="Testing-the-patch"></a><h2>Testing the patch</h2>
<p>The regression tests for each operator live in <i>t/op/</i>, and so we make
a copy of <i>t/op/pack.t</i> to <i>t/op/pack.t~</i>. Now we can add our tests
to the end. First, we'll test that the <code class="inline"><span class="w">U</span></code>
 does indeed create Unicode
strings.</p>
<p>t/op/pack.t has a sensible ok() function, but if it didn't we could use
the one from t/test.pl.</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="functions/require.html">require</a> <span class="q">&#39;./test.pl&#39;</span><span class="sc">;</span></li><li> <span class="i">plan</span><span class="s">(</span> <span class="w">tests</span> <span class="cm">=&gt;</span> <span class="n">159</span> <span class="s">)</span><span class="sc">;</span></li></ol></pre><p>so instead of this:</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="functions/print.html">print</a> <span class="q">&#39;not &#39;</span> unless <span class="q">&quot;1.20.300.4000&quot;</span> eq <a class="l_k" href="functions/sprintf.html">sprintf</a> <span class="q">&quot;%vd&quot;</span><span class="cm">,</span></li><li>                                               <a class="l_k" href="functions/pack.html">pack</a><span class="s">(</span><span class="q">&quot;U*&quot;</span><span class="cm">,</span><span class="n">1</span><span class="cm">,</span><span class="n">20</span><span class="cm">,</span><span class="n">300</span><span class="cm">,</span><span class="n">4000</span><span class="s">)</span><span class="sc">;</span></li><li> <a class="l_k" href="functions/print.html">print</a> <span class="q">&quot;ok $test\n&quot;</span><span class="sc">;</span> <span class="i">$test</span>++<span class="sc">;</span></li></ol></pre><p>we can write the more sensible (see <a href="Test/More.html">Test::More</a> for a full
explanation of is() and other testing functions).</p>
<pre class="verbatim"><ol><li> <span class="i">is</span><span class="s">(</span> <span class="q">&quot;1.20.300.4000&quot;</span><span class="cm">,</span> <a class="l_k" href="functions/sprintf.html">sprintf</a> <span class="q">&quot;%vd&quot;</span><span class="cm">,</span> <a class="l_k" href="functions/pack.html">pack</a><span class="s">(</span><span class="q">&quot;U*&quot;</span><span class="cm">,</span><span class="n">1</span><span class="cm">,</span><span class="n">20</span><span class="cm">,</span><span class="n">300</span><span class="cm">,</span><span class="n">4000</span><span class="s">)</span><span class="cm">,</span></li><li>                                       <span class="q">&quot;U* produces Unicode&quot;</span> <span class="s">)</span><span class="sc">;</span></li></ol></pre><p>Now we'll test that we got that space-at-the-beginning business right:</p>
<pre class="verbatim"><ol><li> <span class="i">is</span><span class="s">(</span> <span class="q">&quot;1.20.300.4000&quot;</span><span class="cm">,</span> <a class="l_k" href="functions/sprintf.html">sprintf</a> <span class="q">&quot;%vd&quot;</span><span class="cm">,</span> <a class="l_k" href="functions/pack.html">pack</a><span class="s">(</span><span class="q">&quot;  U*&quot;</span><span class="cm">,</span><span class="n">1</span><span class="cm">,</span><span class="n">20</span><span class="cm">,</span><span class="n">300</span><span class="cm">,</span><span class="n">4000</span><span class="s">)</span><span class="cm">,</span></li><li>                                     <span class="q">&quot;  with spaces at the beginning&quot;</span> <span class="s">)</span><span class="sc">;</span></li></ol></pre><p>And finally we'll test that we don't make Unicode strings if <code class="inline"><span class="w">U</span></code>
 is
<b>not</b> the first active format:</p>
<pre class="verbatim"><ol><li> <span class="i">isnt</span><span class="s">(</span> <span class="v">v1.20.300.4000</span><span class="cm">,</span> <a class="l_k" href="functions/sprintf.html">sprintf</a> <span class="q">&quot;%vd&quot;</span><span class="cm">,</span> <a class="l_k" href="functions/pack.html">pack</a><span class="s">(</span><span class="q">&quot;C0U*&quot;</span><span class="cm">,</span><span class="n">1</span><span class="cm">,</span><span class="n">20</span><span class="cm">,</span><span class="n">300</span><span class="cm">,</span><span class="n">4000</span><span class="s">)</span><span class="cm">,</span></li><li>                                       <span class="q">&quot;U* not first isn't Unicode&quot;</span> <span class="s">)</span><span class="sc">;</span></li></ol></pre><p>Mustn't forget to change the number of tests which appears at the top,
or else the automated tester will get confused. This will either look
like this:</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="functions/print.html">print</a> <span class="q">&quot;1..156\n&quot;</span><span class="sc">;</span></li></ol></pre><p>or this:</p>
<pre class="verbatim"><ol><li> <span class="i">plan</span><span class="s">(</span> <span class="w">tests</span> <span class="cm">=&gt;</span> <span class="n">156</span> <span class="s">)</span><span class="sc">;</span></li></ol></pre><p>We now compile up Perl, and run it through the test suite. Our new
tests pass, hooray!</p>
<a name="Documenting-the-patch"></a><h2>Documenting the patch</h2>
<p>Finally, the documentation. The job is never done until the paperwork
is over, so let's describe the change we've just made. The relevant
place is <i>pod/perlfunc.pod</i>; again, we make a copy, and then we'll
insert this text in the description of <code class="inline"><a class="l_k" href="functions/pack.html">pack</a></code>:</p>
<pre class="verbatim"><ol><li> =<span class="w">item</span> *</li><li></li><li> <span class="w">If</span> <span class="w">the</span> <span class="w">pattern</span> <span class="w">begins</span> <span class="w">with</span> <span class="w">a</span> <span class="w">C</span><span class="q">&lt;U&gt;</span><span class="cm">,</span> <span class="w">the</span> <span class="w">resulting</span> <span class="w">string</span> <span class="w">will</span> <span class="w">be</span> <span class="w">treated</span></li><li> <span class="w">as</span> <span class="w">UTF</span>-<span class="n">8</span>-<span class="w">encoded</span> <span class="w">Unicode</span>. <span class="w">You</span> <span class="w">can</span> <span class="w">force</span> <span class="w">UTF</span>-<span class="n">8</span> <span class="w">encoding</span> <span class="w">on</span> <span class="w">in</span> <span class="w">a</span> <span class="w">string</span></li><li> <span class="w">with</span> <span class="w">an</span> <span class="w">initial</span> <span class="w">C</span><span class="q">&lt;U0&gt;</span><span class="cm">,</span> and <span class="w">the</span> <span class="w">bytes</span> <span class="w">that</span> <span class="w">follow</span> <span class="w">will</span> <span class="w">be</span> <span class="w">interpreted</span> <span class="w">as</span></li><li> <span class="w">Unicode</span> <span class="w">characters</span>. <span class="w">If</span> <span class="w">you</span> <span class="w">don&#39;t</span> <span class="w">want</span> <span class="w">this</span> <span class="w">to</span> <span class="w">happen</span><span class="cm">,</span> <span class="w">you</span> <span class="w">can</span> <span class="w">begin</span></li><li> <span class="w">your</span> <span class="w">pattern</span> <span class="w">with</span> <span class="w">C</span><span class="q">&lt;C0&gt;</span> <span class="s">(</span>or <span class="w">anything</span> else<span class="s">)</span> <span class="w">to</span> <span class="w">force</span> <span class="w">Perl</span> not <span class="w">to</span> <span class="w">UTF</span>-<span class="n">8</span></li><li> <span class="w">encode</span> <span class="w">your</span> <span class="w">string</span><span class="cm">,</span> and <span class="w">then</span> <span class="w">follow</span> <span class="w">this</span> <span class="w">with</span> <span class="w">a</span> <span class="w">C</span><span class="q">&lt;U*&gt;</span> <span class="w">somewhere</span> <span class="w">in</span> <span class="w">your</span></li><li> <span class="w">pattern</span>.</li></ol></pre><a name="Submit"></a><h2>Submit</h2>
<p>See <a href="perlhack.html">perlhack</a> for details on how to submit this patch.</p>
<a name="AUTHOR"></a><h1>AUTHOR</h1>
<p>This document was originally written by Nathan Torkington, and is
maintained by the perl5-porters mailing list.</p>




  <div id="page_index" class="hud_container">
    <div id="page_index_header" class="hud_header">
      <div id="page_index_close" class="hud_close"><a href="#" onClick="pageIndex.hide();return false;"></a></div>
      <div id="page_index_title" class="hud_title"><span class="hud_span_top">Page index</span></div>
      <div id="page_index_topright" class="hud_topright"></div>
    </div>
    <div id="page_index_content" class="hud_content">
      <ul><li><a href="#NAME">NAME</a><li><a href="#DESCRIPTION">DESCRIPTION</a><li><a href="#EXAMPLE-OF-A-SIMPLE-PATCH">EXAMPLE OF A SIMPLE PATCH</a><ul><li><a href="#Writing-the-patch">Writing the patch</a><li><a href="#Testing-the-patch">Testing the patch</a><li><a href="#Documenting-the-patch">Documenting the patch</a><li><a href="#Submit">Submit</a></ul><li><a href="#AUTHOR">AUTHOR</a></ul>
    </div>
    <div id="page_index_footer" class="hud_footer">
      <div id="page_index_bottomleft" class="hud_bottomleft"></div>
      <div id="page_index_bottom" class="hud_bottom"><span class="hud_span_bottom"></span></div>
      <div id="page_index_resize" class="hud_resize"></div>
    </div>
  </div>


	    &nbsp;
          </div>
          <div id="content_footer">
          </div>
        </div>
        <div class="clear"></div>
      </div>
      
    <div id="footer">
      <div id="footer_content">
        <div id="footer_strapline">
          perldoc.perl.org - Official documentation for the Perl programming language
        </div>
        <div id="footer_links">
          <div id="address">
            <p class="name">Contact details</p>
            <p class="address">
529
	      Site maintained by <a href="mailto:jj@jonallen.info">Jon Allen (JJ)</a><br>
530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582
	    </p>
            <p class="contact">
              Documentation maintained by the <a href="http://lists.cpan.org/showlist.cgi?name=perl5-porters">Perl 5 Porters</a>
            </p>
          </div>
          <ul class="f1">
            <li>Manual
              <ul class="f2">
                <li><a href="index-overview.html">Overview</a>
                <li><a href="index-tutorials.html">Tutorials</a>
                <li><a href="index-faq.html">FAQs</a>
                <li><a href="index-history.html">Changes</a>
              </ul>
            <li>Reference
              <ul class="f2">
                <li><a href="index-language.html">Language</a>
                <li><a href="index-functions.html">Functions</a>
                <li><a href="perlop.html">Operators</a>
                <li><a href="perlvar.html">Variables</a>
              </ul>
            <li>Modules
              <ul class="f2">
                <li><a href="index-modules-A.html">Modules</a>
                <li><a href="index-pragmas.html">Pragmas</a>
                <li><a href="index-utilities.html">Utilities</a>
              </ul>
            <li>Misc
              <ul class="f2">
                <li><a href="index-licence.html">License</a>
                <li><a href="index-internals.html">Internals</a>
                <li><a href="index-platforms.html">Platforms</a>
              </ul>          </ul>
          <div class="clear"></div>
        </div>
      </div>
      <div id="footer_end">
      </div>
    </div>
      
    </div>
      <script language="JavaScript" type="text/javascript" src="static/exploreperl.js"></script>
      <script language="JavaScript" src="static/combined-20100403.js" type="text/javascript"></script>
<script language="JavaScript" type="text/javascript">
  perldoc.setPath(0);
  perldoc.pageName    = 'perlhacktut';
  perldoc.pageAddress = 'perlhacktut.html';
  perldoc.contentPage = 1;
  explorePerl.render();
  explorePerl.addEvents('explore_anchor');
</script>
    
  </body>
</html>