libstdc++-v3/doc/html/manual/dynamic_memory.html

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   3 <html xmlns="http://www.w3.org/1999/xhtml"><head><title>Dynamic Memory</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.75.2"/><meta name="keywords" content="&#10;      ISO C++&#10;    , &#10;      library&#10;    "/><link rel="home" href="../spine.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 align="left"><a accesskey="p" href="support.html">Prev</a> </td><th width="60%" align="center">Chapter 4.
   4   Support
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   6 </th><td align="right"> <a accesskey="n" href="termination.html">Next</a></td></tr></table><hr/></div><div class="section" title="Dynamic Memory"><div class="titlepage"><div><div><h2 class="title"><a id="std.support.memory"/>Dynamic Memory</h2></div></div></div><p>
   7     There are six flavors each of <code class="function">new</code> and
   8     <code class="function">delete</code>, so make certain that you're using the right
   9     ones. Here are quickie descriptions of <code class="function">new</code>:
  10   </p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>
  11         single object form, throwing a
  12         <code class="classname">bad_alloc</code> on errors; this is what most
  13         people are used to using
  14       </p></li><li class="listitem"><p>
  15         Single object "nothrow" form, returning NULL on errors
  16       </p></li><li class="listitem"><p>
  17         Array <code class="function">new</code>, throwing
  18         <code class="classname">bad_alloc</code> on errors
  19       </p></li><li class="listitem"><p>
  20         Array nothrow <code class="function">new</code>, returning
  21         <code class="constant">NULL</code> on errors
  22       </p></li><li class="listitem"><p>
  23         Placement <code class="function">new</code>, which does nothing (like
  24         it's supposed to)
  25       </p></li><li class="listitem"><p>
  26         Placement array <code class="function">new</code>, which also does
  27         nothing
  28       </p></li></ul></div><p>
  29      They are distinguished by the parameters that you pass to them, like
  30      any other overloaded function.  The six flavors of <code class="function">delete</code>
  31      are distinguished the same way, but none of them are allowed to throw
  32      an exception under any circumstances anyhow.  (They match up for
  33      completeness' sake.)
  34    </p><p>
  35      Remember that it is perfectly okay to call <code class="function">delete</code> on a
  36      NULL pointer!  Nothing happens, by definition.  That is not the
  37      same thing as deleting a pointer twice.
  38    </p><p>
  39      By default, if one of the <span class="quote">“<span class="quote">throwing <code class="function">new</code>s</span>”</span> can't
  40      allocate the memory requested, it tosses an instance of a
  41      <code class="classname">bad_alloc</code> exception (or, technically, some class derived
  42      from it).  You can change this by writing your own function (called a
  43      new-handler) and then registering it with <code class="function">set_new_handler()</code>:
  44    </p><pre class="programlisting">
  45    typedef void (*PFV)(void);
  46
  47    static char*  safety;
  48    static PFV    old_handler;
  49
  50    void my_new_handler ()
  51    {
  52        delete[] safety;
  53        popup_window ("Dude, you are running low on heap memory.  You
  54                       should, like, close some windows, or something.
  55                       The next time you run out, we're gonna burn!");
  56        set_new_handler (old_handler);
  57        return;
  58    }
  59
  60    int main ()
  61    {
  62        safety = new char[500000];
  63        old_handler = set_new_handler (&amp;my_new_handler);
  64        ...
  65    }
  66    </pre><p>
  67      <code class="classname">bad_alloc</code> is derived from the base <code class="classname">exception</code>
  68      class defined in Sect1 19.
  69    </p></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="support.html">Prev</a> </td><td align="center"><a accesskey="u" href="support.html">Up</a></td><td align="right"> <a accesskey="n" href="termination.html">Next</a></td></tr><tr><td align="left" valign="top">Chapter 4.
  70   Support
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