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menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-1/b-b-scope-purpose-and-history.html">1. Introduction</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-2/c-b-character-syntax.html">2. Syntax</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-3/d-b-evaluation.html">3. Evaluation and Compilation</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-4/e-b-introduction.html">4. Types and Classes</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-5/f-b-generalized-reference.html">5. Data and Control Flow</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-6/g-b-the-loop-facility.html">6. Iteration</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-7/h-b-object-creation-and-initialization.html">7. Objects</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../category/81-structures-dictionary.html">8. Structures</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-9/j-b-condition-system-concepts.html">9. Conditions</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-10/ba-b-symbol-concepts.html">10. Symbols</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-11/bb-b-package-concepts.html">11. Packages</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-12/bc-b-number-concepts.html">12. Numbers</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-13/bd-b-character-concepts.html">13. Characters</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-14/be-b-cons-concepts.html">14. Conses</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-15/bf-b-array-concepts.html">15. Arrays</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-16/bg-b-string-concepts.html">16. Strings</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-17/bh-b-sequence-concepts.html">17. Sequences</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-18/bi-b-hash-table-concepts.html">18. Hash Tables</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-19/bj-b-overview-of-filenames.html">19. Filenames</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-20/ca-b-file-system-concepts.html">20. Files</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret menu__link--active" aria-expanded="true" href="../cb-b-stream-concepts.html">21. Streams</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="../cb-b-stream-concepts.html">21.1 Stream Concepts</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-2 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--active" aria-expanded="true" tabindex="0" href="../../category/212-streams-dictionary.html">21.2 Streams Dictionary</a><button aria-label="Collapse sidebar category &#x27;21.2 Streams Dictionary&#x27;" type="button" class="clean-btn menu__caret"></button></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="broadcast-stream-streams_function.html">broadcast-stream-streams</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="broadcast-stream_system-class.html">broadcast-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="clear-input_function.html">clear-input</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="close_function.html">close</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="concatenated-stream_system-class.html">concatenated-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" 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class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="finish-output_force-output_clear-output_function.html">finish-output, force-output, clear-output</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="get-output-stream-string_function.html">get-output-stream-string</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="interactive-stream-p_function.html">interactive-stream-p</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="listen_function.html">listen</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="make-broadcast-stream_function.html">make-broadcast-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="make-concatenated-stream_function.html">make-concatenated-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="make-echo-stream_function.html">make-echo-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="make-string-input-stream_function.html">make-string-input-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="make-string-output-stream_function.html">make-string-output-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="make-synonym-stream_function.html">make-synonym-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="make-two-way-stream_function.html">make-two-way-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="open-stream-p_function.html">open-stream-p</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="open_function.html">open</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="peek-char_function.html">peek-char</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="read-byte_function.html">read-byte</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="read-char-no-hang_function.html">read-char-no-hang</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="read-char_function.html">read-char</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="read-line_function.html">read-line</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="read-sequence_function.html">read-sequence</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="stream-element-type_function.html">stream-element-type</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="stream-error-stream_function.html">stream-error-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="stream-external-format_function.html">stream-external-format</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="stream_system-class.html">stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="streamp_function.html">streamp</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="string-stream_system-class.html">string-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="synonym-stream-symbol_function.html">synonym-stream-symbol</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="synonym-stream_system-class.html">synonym-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="terminal-io_variable.html">terminal-io</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="terpri_fresh-line_function.html">terpri, fresh-line</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="two-way-stream_system-class.html">two-way-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="unread-char_function.html">unread-char</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="with-input-from-string_macro.html">with-input-from-string</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="with-open-file_macro.html">with-open-file</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="with-open-stream_macro.html">with-open-stream</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link menu__link--active" aria-current="page" tabindex="0" href="with-output-to-string_macro.html">with-output-to-string</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="write-byte_function.html">write-byte</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="write-char_function.html">write-char</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="write-sequence_function.html">write-sequence</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="write-string_write-line_function.html">write-string, write-line</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="y-or-n-p_yes-or-no-p_function.html">y-or-n-p, yes-or-no-p</a></li></ul></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-22/cc-b-the-lisp-printer.html">22. Printer</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-23/cd-b-reader-concepts.html">23. Reader</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-24/ce-b-system-construction-concepts.html">24. System Construction</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-25/cf-b-the-external-environment.html">25. External Environment</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../environments.html">26. Environments</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../meta-object-protocol.html">27. Meta Object Protocol</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../data-structures.html">28. Data Structures</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../portability/trivial-packages.html">29. Portability</a></div></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-1 menu__list-item"><a class="menu__link" href="../../dictionary-entries.html">dictionary-entries</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-26/intro.html">Glossary</a></div></li></ul></nav></div></div></aside><main class="docMainContainer_TBSr"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_VOVn"><div class="docItemContainer_Djhp"><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Z_bl" aria-label="Breadcrumbs"><ul class="breadcrumbs" itemscope="" itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a aria-label="Home page" class="breadcrumbs__link" href="../../index.html"><svg viewBox="0 0 24 24" class="breadcrumbHomeIcon_YNFT"><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">21. Streams</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item"><a class="breadcrumbs__link" itemprop="item" href="../../category/212-streams-dictionary.html"><span itemprop="name">21.2 Streams Dictionary</span></a><meta itemprop="position" content="2"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">with-output-to-string</span><meta itemprop="position" content="3"></li></ul></nav><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><h1>with-output-to-string</h1>
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<p><strong>with-output-to-string</strong> <span><i>Macro</i></span></p>
<p><strong>Syntax:</strong></p>
<p><span><b>with-output-to-string</b></span> (<em>var</em> &amp;optional <em>string-form</em> &amp;key <em>element-type</em>) <span><i>{declaration}</i></span>* <span><i>{form}</i></span>* → {result}*</p>
<p><strong>Arguments and Values:</strong></p>
<p><em>var</em>—a <em>variable name</em>.</p>
<span><b>with-output-to-string</b></span>
<p><em>string-form</em>—a <span><i>form</i></span> or <span><b>nil</b></span>; if <span><i>non-nil</i></span>, evaluated to produce <span><i>string</i></span>.</p>
<p><span><i>string</i></span>—a <span><i>string</i></span> that has a <span><i>fill pointer</i></span> .</p>
<p><em>element-type</em>—a <span><i>type specifier</i></span> ; evaluated. The default is <span><b>character</b></span>.</p>
<p><span><i>declaration</i></span>—a <span><b>declare</b></span> <span><i>expression</i></span>; not evaluated.</p>
<p><span><i>forms</i></span>—an <span><i>implicit progn</i></span>.</p>
<p><em>results</em>—If a <em>string-form</em> is not supplied or <span><b>nil</b></span>, a <span><i>string</i></span>; otherwise, the <span><i>values</i></span> returned by the <span><i>forms</i></span>.</p>
<p><strong>Description:</strong></p>
<p><span><b>with-output-to-string</b></span> creates a character <em>output stream</em>, performs a series of operations that may send results to this <span><i>stream</i></span>, and then closes the <span><i>stream</i></span>.</p>
<p>The <em>element-type</em> names the <span><i>type</i></span> of the elements of the <span><i>stream</i></span>; a <span><i>stream</i></span> is constructed of the most specialized <span><i>type</i></span> that can accommodate elements of the given <span><i>type</i></span>.</p>
<p>The body is executed as an <span><i>implicit progn</i></span> with <em>var</em> bound to an <em>output string stream</em>. All output to that <span><i>string stream</i></span> is saved in a <span><i>string</i></span>.</p>
<p>If <span><i>string</i></span> is supplied, <em>element-type</em> is ignored, and the output is incrementally appended to <span><i>string</i></span> as if by use of <span><b>vector-push-extend</b></span>.</p>
<p>The <em>output stream</em> is automatically closed on exit from <strong>with-output-from-string</strong>, no matter whether the exit is normal or abnormal. The <em>output string stream</em> to which the <em>variable var</em> is <span><i>bound</i></span> has <span><i>dynamic extent</i></span>; its <span><i>extent</i></span> ends when the <span><i>form</i></span> is exited.</p>
<p>If no <span><i>string</i></span> is provided, then <strong>with-output-from-string</strong> produces a <span><i>stream</i></span> that accepts characters and returns a <span><i>string</i></span> of the indicated <em>element-type</em>. If <span><i>string</i></span> is provided, <span><b>with-output-to-string</b></span> returns the results of evaluating the last <span><i>form</i></span>.</p>
<p>The consequences are undefined if an attempt is made to <span><i>assign</i></span> the <em>variable var</em>.</p>
<p><strong>Examples:</strong></p>
<div class="language-lisp codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-lisp codeBlock_bY9V thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">setq</span><span class="token plain"> fstr </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">make-array</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token lisp-property property" style="color:#36acaa">:element-type</span><span class="token plain"> base-char </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token lisp-property property" style="color:#36acaa">:fill-pointer</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token plain"> </span><span class="token lisp-property property" style="color:#36acaa">:adjustable</span><span class="token plain"> </span><span class="token boolean" style="color:#36acaa">t</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><span class="token string" style="color:#e3116c">&quot;&quot;</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">with-output-to-string</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">s</span><span class="token plain"> fstr</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">format</span><span class="token plain"> s </span><span class="token string" style="color:#e3116c">&quot;heres some output&quot;</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">input-stream-p</span><span class="token plain"> s</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> → false </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">fstr → </span><span class="token string" style="color:#e3116c">&quot;heres some output&quot;</span><span class="token plain"> </span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
<p><strong>Side Effects:</strong></p>
<p>The <span><i>string</i></span> is modified.</p>
<p><strong>Exceptional Situations:</strong></p>
<p>The consequences are undefined if destructive modifications are performed directly on the <span><i>string</i></span> during the <span><i>dynamic extent</i></span> of the call.</p>
<p><strong>See Also:</strong></p>
<p><b>make-string-output-stream</b>, <b>vector-push-extend</b>, Section 3.6 (Traversal Rules and Side Effects) <sup><i></i><b>debug-io</b><i></i><b>,</b> <i></i><b>error-output</b><i></i><b>,</b> <i></i><b>query-io</b><i></i><b>,</b> <i></i><b>standard</b></sup> input<i></i><b>,</b> <i></i><b>standard-output</b><i></i><b>,</b> <i></i><b>trace-output</b><i> Variable</i></p>
<p><strong>Value Type:</strong></p>
<p>For <strong>*standard-input*</strong>: an <em>input stream</em></p>
<p>For <strong>*error-output*</strong>, <strong>*standard-output*</strong>, and <strong>*trace-output*</strong>: an <em>output stream</em>.</p>
<p>For <strong>*debug-io*</strong>, <strong>*query-io*</strong>: a <em>bidirectional stream</em>.</p>
<p><strong>Initial Value:</strong></p>
<p><span><i>implementation-dependent</i></span>, but it must be an <em>open stream</em> that is not a <span><i>generalized synonym stream</i></span> to an <em>I/O customization variables</em> but that might be a <span><i>generalized synonym stream</i></span> to the value of some <em>I/O customization variable</em>. The initial value might also be a <span><i>generalized synonym stream</i></span> to either the <span><i>symbol</i></span> <span><b>*terminal-io*</b></span> or to the <span><i>stream</i></span> that is its <span><i>value</i></span>.</p>
<p><strong>Description:</strong></p>
<p>These <span><i>variables</i></span> are collectively called the <em>standardized I/O customization variables</em>. They can be <span><i>bound</i></span> or <em>assigned</em> in order to change the default destinations for input and/or output used by various <em>standardized operators</em> and facilities.</p>
<p>The <span><i>value</i></span> of <strong>*debug-io*</strong>, called <em>debug I/O</em>, is a <span><i>stream</i></span> to be used for interactive debugging purposes.</p>
<p>The <span><i>value</i></span> of <strong>*error-output*</strong>, called <span><i>error output</i></span>, is a <span><i>stream</i></span> to which warnings and non-interactive error messages should be sent.</p>
<p>The <span><i>value</i></span> of <strong>*query-io*</strong>, called <em>query I/O</em>, is a <em>bidirectional stream</em> to be used when asking questions of the user. The question should be output to this <span><i>stream</i></span>, and the answer read from it.</p>
<p>The <span><i>value</i></span> of <strong>*standard-input*</strong>, called <span><i>standard input</i></span>, is a <span><i>stream</i></span> that is used by many <span><i>operators</i></span> as a default source of input when no specific <em>input stream</em> is explicitly supplied.</p>
<p>The <span><i>value</i></span> of <strong>*standard-output*</strong>, called <span><i>standard output</i></span>, is a <span><i>stream</i></span> that is used by many <span><i>operators</i></span> as a default destination for output when no specific <em>output stream</em> is explicitly supplied.</p>
<p>The <span><i>value</i></span> of <strong>*trace-output*</strong>, called <span><i>trace output</i></span>, is the <span><i>stream</i></span> on which traced functions (see <span><b>trace</b></span>) and the <span><b>time</b></span> <span><i>macro</i></span> print their output.</p>
<p><em></em><strong>debug-io</strong><em></em>**,** <em></em><strong>error-output</strong><em></em>**,** <em></em><strong>query-io</strong><em></em>**,** <em>. . .</em></p>
<p><strong>Examples:</strong></p>
<div class="language-lisp codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-lisp codeBlock_bY9V thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token punctuation" style="color:#393A34">(</span><span class="token car">with-output-to-string</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">\*error-output\*</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">warn</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">&quot;this string is sent to \*error-output\*&quot;</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token string" style="color:#e3116c">&quot;Warning: this string is sent to \*error-output\* </span><br></span><span class="token-line" style="color:#393A34"><span class="token string" style="color:#e3116c">&quot;</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">;The exact format of this string is *implementation-dependent*. </span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">with-input-from-string</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">\*standard-input\* </span><span class="token string" style="color:#e3116c">&quot;1001&quot;</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">+</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">990</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">read</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><span class="token number" style="color:#36acaa">1991</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">progn</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">setq</span><span class="token plain"> out </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">with-output-to-string</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">\*standard-output\*</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">print</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">&quot;print and format t send things to&quot;</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">format</span><span class="token plain"> </span><span class="token boolean" style="color:#36acaa">t</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">&quot;\*standard-output\* now going to a string&quot;</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token lisp-property property" style="color:#36acaa">:done</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token lisp-property property" style="color:#36acaa">:DONE</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">out </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token string" style="color:#e3116c">&quot; </span><br></span><span class="token-line" style="color:#393A34"><span class="token string" style="color:#e3116c">\&quot;print and format t send things to\&quot; \*standard-output\* now going to a string&quot;</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">(</span><span class="token defun keyword" style="color:#00009f">defun</span><span class="token defun"> </span><span class="token defun function" style="color:#d73a49">fact</span><span class="token defun"> </span><span class="token defun punctuation" style="color:#393A34">(</span><span class="token defun arguments argument variable" style="color:#36acaa">n</span><span class="token defun punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">&lt;</span><span class="token plain"> n </span><span class="token number" style="color:#36acaa">2</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">\* n </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">fact</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">-</span><span class="token plain"> n </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">→ FACT </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">trace</span><span class="token plain"> fact</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">FACT</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">;; Of course, the format of traced output is implementation-dependent. </span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">with-output-to-string</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">\*trace-output\*</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">fact</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">3</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token string" style="color:#e3116c">&quot; </span><br></span><span class="token-line" style="color:#393A34"><span class="token string" style="color:#e3116c">1 Enter </span><span class="token string argument" style="color:#e3116c">FACT</span><span class="token string" style="color:#e3116c"> 3 </span><br></span><span class="token-line" style="color:#393A34"><span class="token string" style="color:#e3116c">| 2 Enter </span><span class="token string argument" style="color:#e3116c">FACT</span><span class="token string" style="color:#e3116c"> 2 </span><br></span><span class="token-line" style="color:#393A34"><span class="token string" style="color:#e3116c">| 3 Enter </span><span class="token string argument" style="color:#e3116c">FACT</span><span class="token string" style="color:#e3116c"> 1 </span><br></span><span class="token-line" style="color:#393A34"><span class="token string" style="color:#e3116c">| 3 Exit </span><span class="token string argument" style="color:#e3116c">FACT</span><span class="token string" style="color:#e3116c"> 1 </span><br></span><span class="token-line" style="color:#393A34"><span class="token string" style="color:#e3116c">| 2 Exit </span><span class="token string argument" style="color:#e3116c">FACT</span><span class="token string" style="color:#e3116c"> 2 </span><br></span><span class="token-line" style="color:#393A34"><span class="token string" style="color:#e3116c">1 Exit </span><span class="token string argument" style="color:#e3116c">FACT</span><span class="token string" style="color:#e3116c"> 6&quot;</span><span class="token plain"> </span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
<p><strong>See Also:</strong></p>
<p><span><b>*terminal-io*</b></span>, <span><b>synonym-stream</b></span>, <span><b>time</b></span>, <span><b>trace</b></span>, Chapter 9 (Conditions), Chapter 23 (Reader), Chapter 22 (Printer)</p>
<p><strong>Notes:</strong></p>
<p>The intent of the constraints on the initial <span><i>value</i></span> of the <em>I/O customization variables</em> is to ensure that it is always safe to <span><i>bind</i></span> or <span><i>assign</i></span> such a <span><i>variable</i></span> to the <span><i>value</i></span> of another <em>I/O customization</em></p>
<p><span><i>variable</i></span>, without unduly restricting <span><i>implementation</i></span> flexibility.</p>
<p>It is common for an <span><i>implementation</i></span> to make the initial <span><i>values</i></span> of <strong>*debug-io*</strong> and <strong>*query-io*</strong> be the <em>same stream</em>, and to make the initial <span><i>values</i></span> of <strong>*error-output*</strong> and <strong>*standard-output*</strong> be the <em>same stream</em>.</p>
<p>The functions <span><b>y-or-n-p</b></span> and <span><b>yes-or-no-p</b></span> use <em>query I/O</em> for their input and output.</p>
<p>In the normal <em>Lisp read-eval-print loop</em>, input is read from <span><i>standard input</i></span>. Many input functions, including <span><b>read</b></span> and <span><b>read-char</b></span>, take a <span><i>stream</i></span> argument that defaults to <span><i>standard input</i></span>.</p>
<p>In the normal <em>Lisp read-eval-print loop</em>, output is sent to <span><i>standard output</i></span>. Many output functions, including <span><b>print</b></span> and <span><b>write-char</b></span>, take a <span><i>stream</i></span> argument that defaults to <span><i>standard output</i></span>.</p>
<p>A program that wants, for example, to divert output to a file should do so by <span><i>binding</i></span> <strong>*standard-output*</strong>; that way error messages sent to <strong>*error-output*</strong> can still get to the user by going through <span><b>*terminal-io*</b></span> (if <strong>*error-output*</strong> is bound to <span><b>*terminal-io*</b></span>), which is usually what is desired.</p>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="expanded-reference-with-output-to-string">Expanded Reference: with-output-to-string<a href="with-output-to-string_macro.html#expanded-reference-with-output-to-string" class="hash-link" aria-label="Direct link to Expanded Reference: with-output-to-string" title="Direct link to Expanded Reference: with-output-to-string"></a></h2>
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<div class="language-lisp codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-lisp codeBlock_bY9V thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token punctuation" style="color:#393A34">(</span><span class="token car">with-output-to-string</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">)</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="theme-doc-footer-edit-meta-row row"><div class="col"><a href="https://github.com/lisp-docs/cl-language-reference/tree/main/docs/chap-21/cb-c-dictionary/with-output-to-string_macro.md" target="_blank" rel="noopener noreferrer" class="theme-edit-this-page"><svg fill="currentColor" height="20" width="20" viewBox="0 0 40 40" class="iconEdit_Z9Sw" aria-hidden="true"><g><path d="m34.5 11.7l-3 3.1-6.3-6.3 3.1-3q0.5-0.5 1.2-0.5t1.1 0.5l3.9 3.9q0.5 0.4 0.5 1.1t-0.5 1.2z m-29.5 17.1l18.4-18.5 6.3 6.3-18.4 18.4h-6.3v-6.2z"></path></g></svg>Edit this page</a></div><div class="col lastUpdated_vwxv"><span class="theme-last-updated">Last updated<!-- --> by <b>daninus14</b></span></div></div></footer></article><nav 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