File: bytes.html

package info (click to toggle)
perl-doc-html 5.26.0-4
  • links: PTS, VCS
  • area: main
  • in suites: sid
  • size: 39,400 kB
  • sloc: xml: 36; makefile: 7
file content (529 lines) | stat: -rw-r--r-- 23,326 bytes parent folder | download
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
294
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
430
431
432
433
434
435
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
529
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
  <title>bytes - 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>bytes</h1>
              </div>
              <div id="perl_version">
                Perl 5 version 26.0 documentation
              </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-pragmas.html">Pragmas</a> &gt;
      
    
    bytes
  

            </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>bytes</h1>


  <!--    -->
<ul><li><a href="#NAME">NAME</a><li><a href="#NOTICE">NOTICE</a><li><a href="#SYNOPSIS">SYNOPSIS</a><li><a href="#DESCRIPTION">DESCRIPTION</a><li><a href="#LIMITATIONS">LIMITATIONS</a><li><a href="#SEE-ALSO">SEE ALSO</a></ul><a name="NAME"></a><h1>NAME</h1>
<p>bytes - Perl pragma to expose the individual bytes of characters</p>
<a name="NOTICE"></a><h1>NOTICE</h1>
<p>Because the bytes pragma breaks encapsulation (i.e. it exposes the innards of
how the perl executable currently happens to store a string), the byte values
that result are in an unspecified encoding.</p>
<p><b>Use of this module for anything other than debugging purposes is
strongly discouraged.</b>  If you feel that the functions here within
might be useful for your application, this possibly indicates a
mismatch between your mental model of Perl Unicode and the current
reality. In that case, you may wish to read some of the perl Unicode
documentation: <a href="perluniintro.html">perluniintro</a>, <a href="perlunitut.html">perlunitut</a>, <a href="perlunifaq.html">perlunifaq</a> and
<a href="perlunicode.html">perlunicode</a>.</p>
<a name="SYNOPSIS"></a><h1>SYNOPSIS</h1>
<pre class="verbatim"><ol><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">bytes</span><span class="sc">;</span></li><li>    ... <a class="l_k" href="functions/chr.html">chr</a><span class="s">(</span>...<span class="s">)</span><span class="sc">;</span>       <span class="c"># or bytes::chr</span></li><li>    ... <a class="l_k" href="functions/index.html">index</a><span class="s">(</span>...<span class="s">)</span><span class="sc">;</span>     <span class="c"># or bytes::index</span></li><li>    ... <a class="l_k" href="functions/length.html">length</a><span class="s">(</span>...<span class="s">)</span><span class="sc">;</span>    <span class="c"># or bytes::length</span></li><li>    ... <a class="l_k" href="functions/ord.html">ord</a><span class="s">(</span>...<span class="s">)</span><span class="sc">;</span>       <span class="c"># or bytes::ord</span></li><li>    ... <a class="l_k" href="functions/rindex.html">rindex</a><span class="s">(</span>...<span class="s">)</span><span class="sc">;</span>    <span class="c"># or bytes::rindex</span></li><li>    ... <a class="l_k" href="functions/substr.html">substr</a><span class="s">(</span>...<span class="s">)</span><span class="sc">;</span>    <span class="c"># or bytes::substr</span></li><li>    <a class="l_k" href="functions/no.html">no</a> <span class="w">bytes</span><span class="sc">;</span></li></ol></pre><a name="DESCRIPTION"></a><h1>DESCRIPTION</h1>
<p>Perl's characters are stored internally as sequences of one or more bytes.
This pragma allows for the examination of the individual bytes that together
comprise a character.</p>
<p>Originally the pragma was designed for the loftier goal of helping incorporate
Unicode into Perl, but the approach that used it was found to be defective,
and the one remaining legitimate use is for debugging when you need to
non-destructively examine characters' individual bytes.  Just insert this
pragma temporarily, and remove it after the debugging is finished.</p>
<p>The original usage can be accomplished by explicit (rather than this pragma's
implict) encoding using the <a href="Encode.html">Encode</a> module:</p>
<pre class="verbatim"><ol><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">Encode</span> <span class="q">qw/encode/</span><span class="sc">;</span></li><li></li><li>    <a class="l_k" href="functions/my.html">my</a> <span class="i">$utf8_byte_string</span>   = <span class="w">encode</span> <span class="q">&quot;UTF8&quot;</span><span class="cm">,</span>   <span class="i">$string</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/my.html">my</a> <span class="i">$latin1_byte_string</span> = <span class="w">encode</span> <span class="q">&quot;Latin1&quot;</span><span class="cm">,</span> <span class="i">$string</span><span class="sc">;</span></li></ol></pre><p>Or, if performance is needed and you are only interested in the UTF-8
representation:</p>
<pre class="verbatim"><ol><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">utf8</span><span class="sc">;</span></li><li></li><li>    <span class="i">utf8::encode</span><span class="s">(</span><a class="l_k" href="functions/my.html">my</a> <span class="i">$utf8_byte_string</span> = <span class="i">$string</span><span class="s">)</span><span class="sc">;</span></li></ol></pre><p><code class="inline"><a class="l_k" href="functions/no.html">no</a> <span class="w">bytes</span></code>
 can be used to reverse the effect of <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">bytes</span></code>
 within the
current lexical scope.</p>
<p>As an example, when Perl sees <code class="inline"><span class="i">$x</span> = <a class="l_k" href="functions/chr.html">chr</a><span class="s">(</span><span class="n">400</span><span class="s">)</span></code>
, it encodes the character
in UTF-8 and stores it in <code class="inline"><span class="i">$x</span></code>
. Then it is marked as character data, so,
for instance, <code class="inline"><a class="l_k" href="functions/length.html">length</a> <span class="i">$x</span></code>
 returns <code class="inline"><span class="n">1</span></code>
. However, in the scope of the
<code class="inline"><span class="w">bytes</span></code>
 pragma, <code class="inline"><span class="i">$x</span></code>
 is treated as a series of bytes - the bytes that make
up the UTF8 encoding - and <code class="inline"><a class="l_k" href="functions/length.html">length</a> <span class="i">$x</span></code>
 returns <code class="inline"><span class="n">2</span></code>
:</p>
<pre class="verbatim"><ol><li> <span class="i">$x</span> = <a class="l_k" href="functions/chr.html">chr</a><span class="s">(</span><span class="n">400</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;Length is &quot;</span><span class="cm">,</span> <a class="l_k" href="functions/length.html">length</a> <span class="i">$x</span><span class="cm">,</span> <span class="q">&quot;\n&quot;</span><span class="sc">;</span>     <span class="c"># &quot;Length is 1&quot;</span></li><li> <a class="l_k" href="functions/printf.html">printf</a> <span class="q">&quot;Contents are %vd\n&quot;</span><span class="cm">,</span> <span class="i">$x</span><span class="sc">;</span>         <span class="c"># &quot;Contents are 400&quot;</span></li><li> <span class="s">{</span></li><li>     <a class="l_k" href="functions/use.html">use</a> <span class="w">bytes</span><span class="sc">;</span> <span class="c"># or &quot;require bytes; bytes::length()&quot;</span></li><li>     <a class="l_k" href="functions/print.html">print</a> <span class="q">&quot;Length is &quot;</span><span class="cm">,</span> <a class="l_k" href="functions/length.html">length</a> <span class="i">$x</span><span class="cm">,</span> <span class="q">&quot;\n&quot;</span><span class="sc">;</span> <span class="c"># &quot;Length is 2&quot;</span></li><li>     <a class="l_k" href="functions/printf.html">printf</a> <span class="q">&quot;Contents are %vd\n&quot;</span><span class="cm">,</span> <span class="i">$x</span><span class="sc">;</span>     <span class="c"># &quot;Contents are 198.144 (on</span></li><li>                                          <span class="c"># ASCII platforms)&quot;</span></li><li> <span class="s">}</span></li></ol></pre><p><code class="inline"><a class="l_k" href="functions/chr.html">chr()</a></code>, <code class="inline"><a class="l_k" href="functions/ord.html">ord()</a></code>, <code class="inline"><a class="l_k" href="functions/substr.html">substr()</a></code>, <code class="inline"><a class="l_k" href="functions/index.html">index()</a></code> and <code class="inline"><a class="l_k" href="functions/rindex.html">rindex()</a></code> behave similarly.</p>
<p>For more on the implications, see <a href="perluniintro.html">perluniintro</a> and <a href="perlunicode.html">perlunicode</a>.</p>
<p><code class="inline"><span class="i">bytes::length</span><span class="s">(</span><span class="s">)</span></code>
 is admittedly handy if you need to know the
<b>byte length</b> of a Perl scalar.  But a more modern way is:</p>
<pre class="verbatim"><ol><li>   <a class="l_k" href="functions/use.html">use</a> <span class="w">Encode</span> <span class="q">&#39;encode&#39;</span><span class="sc">;</span></li><li>   <a class="l_k" href="functions/length.html">length</a><span class="s">(</span><span class="i">encode</span><span class="s">(</span><span class="q">&#39;UTF-8&#39;</span><span class="cm">,</span> <span class="i">$scalar</span><span class="s">)</span><span class="s">)</span></li></ol></pre><a name="LIMITATIONS"></a><h1>LIMITATIONS</h1>
<p><code class="inline"><span class="i">bytes::substr</span><span class="s">(</span><span class="s">)</span></code>
 does not work as an <i>lvalue()</i>.</p>
<a name="SEE-ALSO"></a><h1>SEE ALSO</h1>
<p><a href="perluniintro.html">perluniintro</a>, <a href="perlunicode.html">perlunicode</a>, <a href="utf8.html">utf8</a>, <a href="Encode.html">Encode</a></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="#NOTICE">NOTICE</a><li><a href="#SYNOPSIS">SYNOPSIS</a><li><a href="#DESCRIPTION">DESCRIPTION</a><li><a href="#LIMITATIONS">LIMITATIONS</a><li><a href="#SEE-ALSO">SEE ALSO</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">
	      Site maintained by <a href="mailto:jj@jonallen.info">Jon Allen (JJ)</a><br>
	    </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    = 'bytes';
  perldoc.pageAddress = 'bytes.html';
  perldoc.contentPage = 1;
  explorePerl.render();
  explorePerl.addEvents('explore_anchor');
</script>
    
  </body>
</html>