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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>13.3 Byte and String Output</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="extras.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">The Racket Reference</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="model.html" class="tocviewlink" data-pltdoc="x">Language Model</a></td></tr><tr><td align="right">2 </td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3 </td><td><a href="syntax.html" class="tocviewlink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4 </td><td><a href="data.html" class="tocviewlink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5 </td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6 </td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7 </td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12 </td><td><a href="Macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13 </td><td><a href="input-and-output.html" class="tocviewselflink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14 </td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15 </td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16 </td><td><a href="memory.html" class="tocviewlink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17 </td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x">Unsafe Operations</a></td></tr><tr><td align="right">18 </td><td><a href="running.html" c
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that are the UTF-8 encoding of <span class="RktVar">char</span> are written to
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<span class="RktVar">out</span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._write-byte))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-byte%29%29" class="RktValDef RktValLink" data-pltdoc="x">write-byte</a></span></span><span class="hspace"> </span><span class="RktVar">byte</span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">out</span><span class="RktOpt">]</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="void.html#%28def._%28%28quote._~23~25kernel%29._void~3f%29%29" class="RktValLink" data-pltdoc="x">void?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">byte</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="bytestrings.html#%28def._%28%28quote._~23~25kernel%29._byte~3f%29%29" class="RktValLink" data-pltdoc="x">byte?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._output-port~3f%29%29" class="RktValLink" data-pltdoc="x">output-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-output-port%29%29" class="RktValLink" data-pltdoc="x">current-output-port</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Writes a single byte to <span class="RktVar">out</span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._newline))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._newline%29%29" class="RktValDef RktValLink" data-pltdoc="x">newline</a></span></span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">out</span><span class="RktOpt">]</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="void.html#%28def._%28%28quote._~23~25kernel%29._void~3f%29%29" class="RktValLink" data-pltdoc="x">void?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._output-port~3f%29%29" class="RktValLink" data-pltdoc="x">output-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-output-port%29%29" class="RktValLink" data-pltdoc="x">current-output-port</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">The same as <span class="RktPn">(</span><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-char%29%29" class="RktValLink" data-pltdoc="x">write-char</a></span><span class="stt"> </span><span class="Rkt
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index <span class="RktVar">start-pos</span> (inclusive) up to <span class="RktVar">end-pos</span>
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(exclusive). Like <span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._substring%29%29" class="RktValLink" data-pltdoc="x">substring</a></span>, the <span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3afail~3acontract%29%29" class="RktValLink" data-pltdoc="x">exn:fail:contract</a></span> exception is raised
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if <span class="RktVar">start-pos</span> or <span class="RktVar">end-pos</span> is out-of-range for
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<span class="RktVar">str</span>.</div></p><p>The result is the number of characters written to <span class="RktVar">out</span>, which
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is always <span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._-%29%29" class="RktValLink" data-pltdoc="x"><span class="nobreak">-</span></a></span><span class="stt"> </span><span class="RktVar">end-pos</span><span class="stt"> </span><span class="RktVar">start-pos</span><span class="RktPn">)</span>.</p><p>If <span class="RktVar">str</span> is mutable, mutations after <span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-string%29%29" class="RktValLink" data-pltdoc="x">write-string</a></span>
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returns do not affect the characters written to <span class="RktVar">out</span>. (This
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independence from mutation is not a special property of
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<span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-string%29%29" class="RktValLink" data-pltdoc="x">write-string</a></span>, but instead generally true of output
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functions.)</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._write-bytes))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-bytes%29%29" class="RktValDef RktValLink" data-pltdoc="x">write-bytes</a></span></span><span class="hspace"> </span><span class="RktVar">bstr</span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">out</span><span class="hspace"> </span><span class="RktVar">start-pos</span><span class="hspace"> </span><span class="RktVar">end-pos</span><span class="RktOpt">]</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">bstr</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="bytestrings.html#%28def._%28%28quote._~23~25kernel%29._bytes~3f%29%29" class="RktValLink" data-pltdoc="x">bytes?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._output-port~3f%29%29" class="RktValLink" data-pltdoc="x">output-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-output-port%29%29" class="RktValLink" data-pltdoc="x">current-output-port</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">start-pos</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">0</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">end-pos</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="bytestrings.html#%28def._%28%28quote._~23~25kernel%29._bytes-length%29%29" class="RktValLink" data-pltdoc="x">bytes-length</a></span><span class="hspace"> </span><span class="RktVar">bstr</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-string%29%29" class="RktValLink" data-pltdoc="x">write-string</a></span>, but writes bytes instead of characters.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((quote._~23~25kerne
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as many bytes as it can immediately flush. It blocks only if no bytes
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can be flushed immediately. The result is the number of bytes written
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and flushed to <span class="RktVar">out</span>; if <span class="RktVar">start-pos</span> is the same as
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<span class="RktVar">end-pos</span>, then the result can be <span class="RktVal">0</span> (indicating a
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successful flush of any buffered data), otherwise the result is between
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<span class="RktVal">1</span> and <span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._-%29%29" class="RktValLink" data-pltdoc="x"><span class="nobreak">-</span></a></span><span class="stt"> </span><span class="RktVar">end-pos</span><span class="stt"> </span><span class="RktVar">start-pos</span><span class="RktPn">)</span>, inclusive.</div></p><p>The <span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-bytes-avail%29%29" class="RktValLink" data-pltdoc="x">write-bytes-avail</a></span> procedure never drops bytes; if
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<span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-bytes-avail%29%29" class="RktValLink" data-pltdoc="x">write-bytes-avail</a></span> successfully writes some bytes and then
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encounters an error, it suppresses the error and returns the number of
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written bytes. (The error will be triggered by future writes.) If an
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error is encountered before any bytes have been written, an exception
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is raised.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._write-bytes-avail*))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-bytes-avail%2A%29%29" class="RktValDef RktValLink" data-pltdoc="x">write-bytes-avail*</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">bstr</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span><span class="RktOpt">[</span></td><td valign="top"><span class="RktVar">out</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">start-pos</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">end-pos</span><span class="RktOpt">]</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">bstr</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="bytestrings.html#%28def._%28%28quote._~23~25kernel%29._bytes~3f%29%29" class="RktValLink" data-pltdoc="x">bytes?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._output-port~3f%29%29" class="RktValLink" data-pltdoc="x">output-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-output-port%29%29" class="RktValLink" data-pltdoc="x">current-output-port</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">start-pos</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">0</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">end-pos</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span><span class="hspace">
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if the port contains buffered data that cannot be written immediately,
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and returns <span class="RktVal">0</span> if the port’s internal buffer (if any) is
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flushed but no additional bytes can be written immediately.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._write-bytes-avail/enable-break))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-bytes-avail%2Fenable-break%29%29" class="RktValDef RktValLink" data-pltdoc="x">write-bytes-avail/enable-break</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">bstr</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span><span class="RktOpt">[</span></td><td valign="top"><span class="RktVar">out</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">start-pos</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">end-pos</span><span class="RktOpt">]</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">bstr</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="bytestrings.html#%28def._%28%28quote._~23~25kernel%29._bytes~3f%29%29" class="RktValLink" data-pltdoc="x">bytes?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._output-port~3f%29%29" class="RktValLink" data-pltdoc="x">output-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-output-port%29%29" class="RktValLink" data-pltdoc="x">current-output-port</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">start-pos</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">0</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">end-pos</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="bytestrings.html#%28def._%28%28quote._~23~25kernel%29._bytes-length%29%29" class="RktValLink" data-pltdoc="x">bytes-length</a></span><span c
|
||
|
|
the write. The procedure provides a guarantee about the interaction of
|
||
|
|
writing and breaks: if breaking is disabled when
|
||
|
|
<span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-bytes-avail%2Fenable-break%29%29" class="RktValLink" data-pltdoc="x">write-bytes-avail/enable-break</a></span> is called, and if the
|
||
|
|
<span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3abreak%29%29" class="RktValLink" data-pltdoc="x">exn:break</a></span> exception is raised as a result of the call, then
|
||
|
|
no bytes will have been written to <span class="RktVar">out</span>. See also
|
||
|
|
<a href="breakhandler.html" data-pltdoc="x">Breaks</a>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._write-special))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-special%29%29" class="RktValDef RktValLink" data-pltdoc="x">write-special</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">out</span><span class="RktOpt">]</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._output-port~3f%29%29" class="RktValLink" data-pltdoc="x">output-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-output-port%29%29" class="RktValLink" data-pltdoc="x">current-output-port</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Writes <span class="RktVar">v</span> directly to <span class="RktVar">out</span> if the port supports
|
||
|
|
special writes, or raises <span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3afail~3acontract%29%29" class="RktValLink" data-pltdoc="x">exn:fail:contract</a></span> if the port does
|
||
|
|
not support special write. The result is always <span class="RktVal">#t</span>,
|
||
|
|
indicating that the write succeeded.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._write-special-avail*))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-special-avail%2A%29%29" class="RktValDef RktValLink" data-pltdoc="x">write-special-avail*</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">out</span><span class="RktOpt">]</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._output-port~3f%29%29" class="RktValLink" data-pltdoc="x">output-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-output-port%29%29" class="RktValLink" data-pltdoc="x">current-output-port</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-special%29%29" class="RktValLink" data-pltdoc="x">write-special</a></span>, but without blocking. If <span class="RktVar">v</span>
|
||
|
|
cannot be written immediately, the result is <span class="RktVal">#f</span> without
|
||
|
|
writing <span class="RktVar">v</span>, otherwise the result is <span class="RktVal">#t</span> and <span class="RktVar">v</span>
|
||
|
|
is written.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._write-bytes-avail-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-bytes-avail-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">write-bytes-avail-evt</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">bstr</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span><span class="RktOpt">[</span></td><td valign="top"><span class="RktVar">out</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">start-pos</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">end-pos</span><span class="RktOpt">]</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">→</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktSym"><a href="sync.html#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">bstr</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="bytestrings.html#%28def._%28%28quote._~23~25kernel%29._bytes~3f%29%29" class="RktValLink" data-pltdoc="x">bytes?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._output-port~3f%29%29" class="RktValLink" data-pltdoc="x">output-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-output-port%29%29" class="RktValLink" data-pltdoc="x">current-output-port</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">start-pos</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">0</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">end-pos</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23
|
||
|
|
immediately, it returns a synchronizable event (see
|
||
|
|
<a href="sync.html" data-pltdoc="x">Events</a>). The <span class="RktVar">out</span> must support atomic writes, as
|
||
|
|
indicated by <span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._port-writes-atomic~3f%29%29" class="RktValLink" data-pltdoc="x">port-writes-atomic?</a></span>.</div></p><p>Synchronizing on the object starts a write from <span class="RktVar">bstr</span>, and the
|
||
|
|
event becomes ready when bytes are written (unbuffered) to the
|
||
|
|
port. If <span class="RktVar">start-pos</span> and <span class="RktVar">end-pos</span> are the same, then
|
||
|
|
the synchronization result is <span class="RktVal">0</span> when the port’s internal
|
||
|
|
buffer (if any) is flushed, otherwise the result is a positive exact
|
||
|
|
integer. If the event is not selected in a synchronization, then no
|
||
|
|
bytes will have been written to <span class="RktVar">out</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._write-special-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-special-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">write-special-evt</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">out</span><span class="RktOpt">]</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="sync.html#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._output-port~3f%29%29" class="RktValLink" data-pltdoc="x">output-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-output-port%29%29" class="RktValLink" data-pltdoc="x">current-output-port</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Similar to <span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-special%29%29" class="RktValLink" data-pltdoc="x">write-special</a></span>, but instead of writing the special
|
||
|
|
value immediately, it returns a synchronizable event (see
|
||
|
|
<a href="sync.html" data-pltdoc="x">Events</a>). The <span class="RktVar">out</span> must support atomic writes, as
|
||
|
|
indicated by <span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._port-writes-atomic~3f%29%29" class="RktValLink" data-pltdoc="x">port-writes-atomic?</a></span>.</div></p><p>Synchronizing on the object starts a write of the special value, and
|
||
|
|
the event becomes ready when the value is written (unbuffered) to the
|
||
|
|
port. If the event is not selected in a synchronization, then no value
|
||
|
|
will have been written to <span class="RktVar">out</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._port-writes-atomic~3f))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._port-writes-atomic~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">port-writes-atomic?</a></span></span><span class="hspace"> </span><span class="RktVar">out</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._output-port~3f%29%29" class="RktValLink" data-pltdoc="x">output-port?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVal">#t</span> if <span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-bytes-avail%2Fenable-break%29%29" class="RktValLink" data-pltdoc="x">write-bytes-avail/enable-break</a></span> can
|
||
|
|
provide an exclusive-or guarantee (break or write, but not both) for
|
||
|
|
<span class="RktVar">out</span>, and if the port can be used with procedures like
|
||
|
|
<span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-bytes-avail-evt%29%29" class="RktValLink" data-pltdoc="x">write-bytes-avail-evt</a></span>. Racket’s file-stream ports, pipes,
|
||
|
|
string ports, and TCP ports all support atomic writes; ports created
|
||
|
|
with <span class="RktSym"><a href="customport.html#%28def._%28%28quote._~23~25kernel%29._make-output-port%29%29" class="RktValLink" data-pltdoc="x">make-output-port</a></span> (see <a href="customport.html" data-pltdoc="x">Custom Ports</a>) may
|
||
|
|
support atomic writes.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._port-writes-special~3f))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._port-writes-special~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">port-writes-special?</a></span></span><span class="hspace"> </span><span class="RktVar">out</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._output-port~3f%29%29" class="RktValLink" data-pltdoc="x">output-port?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVal">#t</span> if procedures like <span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-special%29%29" class="RktValLink" data-pltdoc="x">write-special</a></span> can
|
||
|
|
write arbitrary values to the port. Racket’s file-stream ports,
|
||
|
|
pipes, string ports, and TCP ports all reject special values, but
|
||
|
|
ports created with <span class="RktSym"><a href="customport.html#%28def._%28%28quote._~23~25kernel%29._make-output-port%29%29" class="RktValLink" data-pltdoc="x">make-output-port</a></span> (see
|
||
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<a href="customport.html" data-pltdoc="x">Custom Ports</a>) may support them.</div></p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="Byte_and_String_Input.html" title="backward to "13.2 Byte and String Input"" data-pltdoc="x">← prev</a> <a href="input-and-output.html" title="up to "13 Input and Output"" data-pltdoc="x">up</a> <a href="Reading.html" title="forward to "13.4 Reading"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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