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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>8.5 Bytes, Characters, and Encodings</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">►</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x"><span style="font-weight: bold">The Racket Guide</span></a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="intro.html" class="tocviewlink" data-pltdoc="x">Welcome to Racket</a></td></tr><tr><td align="right">2 </td><td><a href="to-scheme.html" class="tocviewlink" data-pltdoc="x">Racket Essentials</a></td></tr><tr><td align="right">3 </td><td><a href="datatypes.html" class="tocviewlink" data-pltdoc="x">Built-<wbr></wbr>In Datatypes</a></td></tr><tr><td align="right">4 </td><td><a href="scheme-forms.html" class="tocviewlink" data-pltdoc="x">Expressions and Definitions</a></td></tr><tr><td align="right">5 </td><td><a href="define-struct.html" class="tocviewlink" data-pltdoc="x">Programmer-<wbr></wbr>Defined Datatypes</a></td></tr><tr><td align="right">6 </td><td><a href="modules.html" class="tocviewlink" data-pltdoc="x">Modules</a></td></tr><tr><td align="right">7 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">8 </td><td><a href="i_o.html" class="tocviewselflink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">9 </td><td><a href="regexp.html" class="tocviewlink" data-pltdoc="x">Regular Expressions</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Exceptions and Control</a></td></tr><tr><td align="right">11 </td><td><a href="for.html" class="tocviewlink" data-pltdoc="x">Iterations and Comprehensions</a></td></tr><tr><td align="right">12 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">13 </td><td><a href="classes.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">14 </td><td><a href="units.html" class="tocviewlink" data-pltdoc="x">Units (Components)</a></td></tr><tr><td align="right">15 </td><td><a href="reflection.html" class="tocviewlink" data-pltdoc="x">Reflection and Dynamic Evaluation</a></td></tr><tr><td align="right">16 </td><td><a href="macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">17 </td><td><a href="languages.html" class="tocviewlink" data-pltdoc="x">Creating Languages</a></td></tr><tr><td align="right">18 </td><td><a 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class="tocviewlink" data-pltdoc="x">Bibliography</a></td></tr><tr><td align="right"></td><td><a href="doc-index.html" class="tocviewlink" data-pltdoc="x">Index</a></td></tr></table></div></div><div class="tocviewlist"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_1");">▼</a></td><td>8 </td><td><a href="i_o.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr></table><div class="tocviewsublistbottom" style="display: block;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">8.1 </td><td><a href="ports.html" class="tocviewlink" data-pltdoc="x">Varieties of Ports</a></td></tr><tr><td align="right">8.2 </td><td><a href="default-ports.html" class="tocviewlink" data-pltdoc="x">Default Ports</a></td></tr><tr><td align="right">8.3 </td><td><a href="read-write.html" class="tocviewlink" data-pltdoc="x">Reading and Writing Racket Data</a></td></tr><tr><td align="right">8.4 </td><td><a href="serialization.html" class="tocviewlink" data-pltdoc="x">Datatypes and Serialization</a></td></tr><tr><td align="right">8.5 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Bytes, Characters, and Encodings</a></td></tr><tr><td align="right">8.6 </td><td><a href="io-patterns.html" class="tocviewlink" data-pltdoc="x">I/<span class="mywbr"> </span>O Patterns</a></td></tr></table></div></div></div></div><div class="maincolumn"><div class="main"><div class="navsettop"><span class="navleft"><form class="searchform"><input class="searchbox" style="color: #888;" type="text" value="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "6.1", "../");" onfocus="this.style.color="black"; this.style.textAlign="left"; if (this.value == "...search manuals...") this.value="";" onblur="if (this.value.match(/^ *$/)) { this.style.color="#888"; this.style.textAlign="center"; this.value="...search manuals..."; }"/></form> <a href="../index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("6.1");">top</a></span><span class="navright"> <a href="serialization.html" title="backward to "8.4 Datatypes and Serialization"" data-pltdoc="x">← prev</a> <a href="i_o.html" title="up to "8 Input and Output"" data-pltdoc="x">up</a> <a href="io-patterns.html" title="forward to "8.6 I/O Patterns"" data-pltdoc="x">next →</a></span> </div><h4 x-source-module="(lib "scribblings/guide/guide.scrbl")" x-part-tag=""encodings"">8.5<tt> </tt><a name="(part._encodings)"></a>Bytes, Characters, and Encodings</h4><p>Functions like <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-line%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read-line</a></span>, <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Reading.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read</a></span>, <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Writing.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._display%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">display</a></span>,
and <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Writing.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._write%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">write</a></span> all work in terms of <a href="characters.html#%28tech._character%29" class="techoutside" data-pltdoc="x"><span class="techinside">characters</span></a> (which
correspond to Unicode scalar values). Conceptually, they are
implemented in terms of <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-char%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read-char</a></span> and <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Output.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._write-char%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">write-char</a></span>.</p><p>More primitively, ports read and write <a href="bytestrings.html#%28tech._byte%29" class="techoutside" data-pltdoc="x"><span class="techinside">bytes</span></a>, instead of
<a href="characters.html#%28tech._character%29" class="techoutside" data-pltdoc="x"><span class="techinside">characters</span></a>. The functions <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-byte%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read-byte</a></span> and
<span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Output.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._write-byte%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">write-byte</a></span> read and write raw bytes. Other functions, such as
<span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-bytes-line%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read-bytes-line</a></span>, build on top of byte operations instead of
character operations.</p><p>In fact, the <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-char%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read-char</a></span> and <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Output.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._write-char%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">write-char</a></span> functions are
conceptually implemented in terms of <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-byte%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read-byte</a></span> and
<span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Output.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._write-byte%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">write-byte</a></span>. When a single byte’s value is less than 128, then
it corresponds to an ASCII character. Any other byte is treated as
part of a UTF-8 sequence, where UTF-8 is a particular standard way of
encoding Unicode scalar values in bytes (which has the nice property
that ASCII characters are encoded as themselves). Thus, a single
<span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-char%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read-char</a></span> may call <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-byte%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read-byte</a></span> multiple times, and a
single <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Output.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._write-char%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">write-char</a></span> may generate multiple output bytes.</p><p>The <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-char%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read-char</a></span> and <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Output.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._write-char%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">write-char</a></span> operations
<span style="font-style: italic">always</span> use a UTF-8 encoding. If you have a text stream that
uses a different encoding, or if you want to generate a text stream in
a different encoding, use <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=port-lib.html%23%2528def._%2528%2528lib._racket%252Fport..rkt%2529._reencode-input-port%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">reencode-input-port</a></span> or
<span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=port-lib.html%23%2528def._%2528%2528lib._racket%252Fport..rkt%2529._reencode-output-port%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">reencode-output-port</a></span>. The <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=port-lib.html%23%2528def._%2528%2528lib._racket%252Fport..rkt%2529._reencode-input-port%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">reencode-input-port</a></span>
function converts an input stream from an encoding that you specify
into a UTF-8 stream; that way, <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-char%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read-char</a></span> sees UTF-8
encodings, even though the original used a different encoding. Beware,
however, that <span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-byte%2529%2529&version=6.1" class="RktValLink Sq" data-pltdoc="x">read-byte</a></span> also sees the re-encoded data,
instead of the original byte stream.</p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" style="color: #888;" type="text" value="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "6.1", "../");" onfocus="this.style.color="black"; this.style.textAlign="left"; if (this.value == "...search manuals...") this.value="";" onblur="if (this.value.match(/^ *$/)) { this.style.color="#888"; this.style.textAlign="center"; this.value="...search manuals..."; }"/></form> <a href="../index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("6.1");">top</a></span><span class="navright"> <a href="serialization.html" title="backward to "8.4 Datatypes and Serialization"" data-pltdoc="x">← prev</a> <a href="i_o.html" title="up to "8 Input and Output"" data-pltdoc="x">up</a> <a href="io-patterns.html" title="forward to "8.6 I/O Patterns"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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