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HTML
71 lines
4.7 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!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/html; charset=UTF-8" /><title>Dynamic Memory</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.78.1" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="support.html" title="Chapter 4. Support" /><link rel="prev" href="support.html" title="Chapter 4. Support" /><link rel="next" href="termination.html" title="Termination" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Dynamic Memory</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="support.html">Prev</a> </td><th width="60%" align="center">Chapter 4.
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Support
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</th><td width="20%" align="right"> <a accesskey="n" href="termination.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="std.support.memory"></a>Dynamic Memory</h2></div></div></div><p>
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There are six flavors each of <code class="function">new</code> and
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<code class="function">delete</code>, so make certain that you're using the right
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ones. Here are quickie descriptions of <code class="function">new</code>:
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</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
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single object form, throwing a
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<code class="classname">bad_alloc</code> on errors; this is what most
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people are used to using
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</p></li><li class="listitem"><p>
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Single object "nothrow" form, returning NULL on errors
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</p></li><li class="listitem"><p>
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Array <code class="function">new</code>, throwing
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<code class="classname">bad_alloc</code> on errors
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</p></li><li class="listitem"><p>
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Array nothrow <code class="function">new</code>, returning
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<code class="constant">NULL</code> on errors
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</p></li><li class="listitem"><p>
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Placement <code class="function">new</code>, which does nothing (like
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it's supposed to)
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</p></li><li class="listitem"><p>
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Placement array <code class="function">new</code>, which also does
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nothing
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</p></li></ul></div><p>
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They are distinguished by the parameters that you pass to them, like
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any other overloaded function. The six flavors of <code class="function">delete</code>
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are distinguished the same way, but none of them are allowed to throw
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an exception under any circumstances anyhow. (They match up for
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completeness' sake.)
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</p><p>
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Remember that it is perfectly okay to call <code class="function">delete</code> on a
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NULL pointer! Nothing happens, by definition. That is not the
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same thing as deleting a pointer twice.
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</p><p>
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By default, if one of the <span class="quote">“<span class="quote">throwing <code class="function">new</code>s</span>”</span> can't
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allocate the memory requested, it tosses an instance of a
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<code class="classname">bad_alloc</code> exception (or, technically, some class derived
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from it). You can change this by writing your own function (called a
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new-handler) and then registering it with <code class="function">set_new_handler()</code>:
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</p><pre class="programlisting">
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typedef void (*PFV)(void);
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static char* safety;
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static PFV old_handler;
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void my_new_handler ()
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{
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delete[] safety;
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popup_window ("Dude, you are running low on heap memory. You
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should, like, close some windows, or something.
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The next time you run out, we're gonna burn!");
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set_new_handler (old_handler);
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return;
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}
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int main ()
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{
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safety = new char[500000];
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old_handler = set_new_handler (&my_new_handler);
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...
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}
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</pre><p>
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<code class="classname">bad_alloc</code> is derived from the base <code class="classname">exception</code>
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class defined in Sect1 19.
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</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="support.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="support.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="termination.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 4.
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Support
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</td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Termination</td></tr></table></div></body></html> |