<!-- HTML header for doxygen 1.8.7--> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/xhtml;charset=UTF-8"/> <meta http-equiv="X-UA-Compatible" content="IE=9"/> <meta name="generator" content="Doxygen 1.6.3"/> <!--BEGIN PROJECT_NAME--><title>avr-libc: avr-libc: <setjmp.h>: Non-local goto</title><!--END PROJECT_NAME--> <!--BEGIN !PROJECT_NAME--><title>avr-libc: <setjmp.h>: Non-local goto</title><!--END !PROJECT_NAME--> <link href="$relpath^tabs.css" rel="stylesheet" type="text/css"/> <script type="text/javascript" src="$relpath^jquery.js"></script> <script type="text/javascript" src="$relpath^dynsections.js"></script> $treeview $search $mathjax <link href="$relpath^$stylesheet" rel="stylesheet" type="text/css" /> $extrastylesheet </head> <body> <div id="top"><!-- do not remove this div, it is closed by doxygen! --> <!--BEGIN TITLEAREA--> <div id="titlearea"> <table cellspacing="0" cellpadding="0"> <tbody> <tr style="height: 56px;"> <!--BEGIN PROJECT_LOGO--> <td id="projectlogo"><img alt="Logo" src="$relpath^$projectlogo"/></td> <!--END PROJECT_LOGO--> <!--BEGIN PROJECT_NAME--> <td style="padding-left: 0.5em;"> <div id="projectname">avr-libc <!--BEGIN PROJECT_NUMBER--> <span id="projectnumber">2.0.0</span><!--END PROJECT_NUMBER--> </div> <!--BEGIN PROJECT_BRIEF--><div id="projectbrief">$projectbrief</div><!--END PROJECT_BRIEF--> </td> <!--END PROJECT_NAME--> <!--BEGIN !PROJECT_NAME--> <!--BEGIN PROJECT_BRIEF--> <td style="padding-left: 0.5em;"> <div id="projectbrief">$projectbrief</div> </td> <!--END PROJECT_BRIEF--> <!--END !PROJECT_NAME--> <!--BEGIN DISABLE_INDEX--> <!--BEGIN SEARCHENGINE--> <td>$searchbox</td> <!--END SEARCHENGINE--> <!--END DISABLE_INDEX--> </tr> </tbody> </table> <table> <tr> <td align="left"><a href="http://www.nongnu.org/avr-libc/"><h2>AVR Libc Home Page</h2></a></td> <td align="center" colspan=4><img src="avrs.png" alt="AVRs" align="middle" border="0"></td> <td align="right"><a href="https://savannah.nongnu.org/projects/avr-libc/"><h2>AVR Libc Development Pages</h2></a></td> </tr> <tr> <td align="center" width="20%"><a href="index.html"><h2>Main Page</h2></a></td> <td align="center" width="20%"><a href="pages.html"><h2>User Manual</h2></a></td> <td align="center" width="20%"><a href="modules.html"><h2>Library Reference</h2></a></td> <td align="center" width="20%"><a href="FAQ.html"><h2>FAQ</h2></a></td> <td align="center" width="20%"><a href="group__demos.html"><h2>Example Projects</h2></a></td> </tr> </table> </div> <!--END TITLEAREA--> <!-- end header part --> <!-- Generated by Doxygen 1.6.3 --> <script type="text/javascript"><!-- var searchBox = new SearchBox("searchBox", "search",false,'Search'); --></script> <div class="contents"> <h1><setjmp.h>: Non-local goto</h1><table border="0" cellpadding="0" cellspacing="0"> <tr><td colspan="2"><h2>Functions</h2></td></tr> <tr><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6">setjmp</a> (jmp_buf __jmpb)</td></tr> <tr><td class="memItemLeft" align="right" valign="top">void </td><td class="memItemRight" valign="bottom"><a class="el" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf">longjmp</a> (jmp_buf __jmpb, int __ret) __ATTR_NORETURN__</td></tr> </table> <hr/><a name="_details"></a><h2>Detailed Description</h2> <p>While the C language has the dreaded <code>goto</code> statement, it can only be used to jump to a label in the same (local) function. In order to jump directly to another (non-local) function, the C library provides the <a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp()</a> and <a class="el" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf" title="Non-local jump to a saved stack context.">longjmp()</a> functions. <a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp()</a> and <a class="el" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf" title="Non-local jump to a saved stack context.">longjmp()</a> are useful for dealing with errors and interrupts encountered in a low-level subroutine of a program.</p> <dl class="note"><dt><b>Note:</b></dt><dd><a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp()</a> and <a class="el" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf" title="Non-local jump to a saved stack context.">longjmp()</a> make programs hard to understand and maintain. If possible, an alternative should be used.</dd> <dd> <a class="el" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf" title="Non-local jump to a saved stack context.">longjmp()</a> can destroy changes made to global register variables (see <a class="el" href="FAQ.html#faq_regbind">How to permanently bind a variable to a register?</a>).</dd></dl> <p>For a very detailed discussion of <a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp()</a>/longjmp(), see Chapter 7 of <em>Advanced Programming in the UNIX Environment</em>, by W. Richard Stevens.</p> <p>Example:</p> <div class="fragment"><pre class="fragment"><span class="preprocessor"> #include <<a class="code" href="setjmp_8h.html">setjmp.h</a>></span> jmp_buf env; <span class="keywordtype">int</span> main (<span class="keywordtype">void</span>) { <span class="keywordflow">if</span> (<a class="code" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp</a> (env)) { ... handle error ... } <span class="keywordflow">while</span> (1) { ... main processing loop which calls foo() some where ... } } ... <span class="keywordtype">void</span> foo (<span class="keywordtype">void</span>) { ... blah, blah, blah ... <span class="keywordflow">if</span> (err) { <a class="code" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf" title="Non-local jump to a saved stack context.">longjmp</a> (env, 1); } } </pre></div> <hr/><h2>Function Documentation</h2> <a class="anchor" id="ga87f44eafaab5ec0ef8f5a11a8b853acf"></a><!-- doxytag: member="setjmp.h::longjmp" ref="ga87f44eafaab5ec0ef8f5a11a8b853acf" args="(jmp_buf __jmpb, int __ret) __ATTR_NORETURN__" --> <div class="memitem"> <div class="memproto"> <table class="memname"> <tr> <td class="memname">void longjmp </td> <td>(</td> <td class="paramtype">jmp_buf </td> <td class="paramname"> <em>__jmpb</em>, </td> </tr> <tr> <td class="paramkey"></td> <td></td> <td class="paramtype">int </td> <td class="paramname"> <em>__ret</em></td><td> </td> </tr> <tr> <td></td> <td>)</td> <td></td><td></td><td></td> </tr> </table> </div> <div class="memdoc"> <p>Non-local jump to a saved stack context. </p> <div class="fragment"><pre class="fragment"><span class="preprocessor"> #include <<a class="code" href="setjmp_8h.html">setjmp.h</a>></span> </pre></div><p><a class="el" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf" title="Non-local jump to a saved stack context.">longjmp()</a> restores the environment saved by the last call of <a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp()</a> with the corresponding <em>__jmpb</em> argument. After <a class="el" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf" title="Non-local jump to a saved stack context.">longjmp()</a> is completed, program execution continues as if the corresponding call of <a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp()</a> had just returned the value <em>__ret</em>.</p> <dl class="note"><dt><b>Note:</b></dt><dd><a class="el" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf" title="Non-local jump to a saved stack context.">longjmp()</a> cannot cause 0 to be returned. If <a class="el" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf" title="Non-local jump to a saved stack context.">longjmp()</a> is invoked with a second argument of 0, 1 will be returned instead.</dd></dl> <dl><dt><b>Parameters:</b></dt><dd> <table border="0" cellspacing="2" cellpadding="0"> <tr><td valign="top"></td><td valign="top"><em>__jmpb</em> </td><td>Information saved by a previous call to <a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp()</a>. </td></tr> <tr><td valign="top"></td><td valign="top"><em>__ret</em> </td><td>Value to return to the caller of <a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp()</a>.</td></tr> </table> </dd> </dl> <dl class="return"><dt><b>Returns:</b></dt><dd>This function never returns. </dd></dl> </div> </div> <a class="anchor" id="ga2687c5ef7a3f376db90908999a9a7fc6"></a><!-- doxytag: member="setjmp.h::setjmp" ref="ga2687c5ef7a3f376db90908999a9a7fc6" args="(jmp_buf __jmpb)" --> <div class="memitem"> <div class="memproto"> <table class="memname"> <tr> <td class="memname">int setjmp </td> <td>(</td> <td class="paramtype">jmp_buf </td> <td class="paramname"> <em>__jmpb</em></td> <td> ) </td> <td></td> </tr> </table> </div> <div class="memdoc"> <p>Save stack context for non-local goto. </p> <div class="fragment"><pre class="fragment"><span class="preprocessor"> #include <<a class="code" href="setjmp_8h.html">setjmp.h</a>></span> </pre></div><p><a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp()</a> saves the stack context/environment in <em>__jmpb</em> for later use by <a class="el" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf" title="Non-local jump to a saved stack context.">longjmp()</a>. The stack context will be invalidated if the function which called <a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp()</a> returns.</p> <dl><dt><b>Parameters:</b></dt><dd> <table border="0" cellspacing="2" cellpadding="0"> <tr><td valign="top"></td><td valign="top"><em>__jmpb</em> </td><td>Variable of type <code>jmp_buf</code> which holds the stack information such that the environment can be restored.</td></tr> </table> </dd> </dl> <dl class="return"><dt><b>Returns:</b></dt><dd><a class="el" href="group__setjmp.html#ga2687c5ef7a3f376db90908999a9a7fc6" title="Save stack context for non-local goto.">setjmp()</a> returns 0 if returning directly, and non-zero when returning from <a class="el" href="group__setjmp.html#ga87f44eafaab5ec0ef8f5a11a8b853acf" title="Non-local jump to a saved stack context.">longjmp()</a> using the saved context. </dd></dl> </div> </div> </div> <!--- window showing the filter options --> <div id="MSearchSelectWindow" onmouseover="return searchBox.OnSearchSelectShow()" onmouseout="return searchBox.OnSearchSelectHide()" onkeydown="return searchBox.OnSearchSelectKey(event)"> <a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(0)"><span class="SelectionMark"> </span>All</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(1)"><span class="SelectionMark"> </span>Data Structures</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(2)"><span class="SelectionMark"> </span>Files</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(3)"><span class="SelectionMark"> </span>Functions</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(4)"><span class="SelectionMark"> </span>Variables</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(5)"><span class="SelectionMark"> </span>Typedefs</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(6)"><span class="SelectionMark"> </span>Enumerations</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(7)"><span class="SelectionMark"> </span>Defines</a></div> <!-- iframe showing the search results (closed by default) --> <div id="MSearchResultsWindow"> <iframe src="" frameborder="0" name="MSearchResults" id="MSearchResults"> </iframe> </div> <!-- HTML footer for doxygen 1.8.7--> <!-- start footer part --> <!--BEGIN GENERATE_TREEVIEW--> <div id="nav-path" class="navpath"><!-- id is needed for treeview function! --> <ul> $navpath <li class="footer">$generatedby <a href="http://www.doxygen.org/index.html"> <img class="footer" src="$relpath^doxygen.png" alt="doxygen"/></a> 1.6.3 </li> </ul> </div> <!--END GENERATE_TREEVIEW--> <!--BEGIN !GENERATE_TREEVIEW--> <hr class="footer"/><address class="footer"><small> $generatedby  <a href="http://www.doxygen.org/index.html"> <img class="footer" src="$relpath^doxygen.png" alt="doxygen"/> </a> 1.6.3 </small></address> <!--END !GENERATE_TREEVIEW--> </body> </html>