libstdc++-v3/doc/html/manual/bk01pt02ch05.html

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   4     There are six flavors each of <code class="function">new</code> and
   5     <code class="function">delete</code>, so make certain that you're using the right
   6     ones. Here are quickie descriptions of <code class="function">new</code>:
   7   </p><div class="itemizedlist"><ul type="disc"><li><p>
   8         single object form, throwing a
   9         <code class="classname">bad_alloc</code> on errors; this is what most
  10         people are used to using
  11       </p></li><li><p>
  12         Single object "nothrow" form, returning NULL on errors
  13       </p></li><li><p>
  14         Array <code class="function">new</code>, throwing
  15         <code class="classname">bad_alloc</code> on errors
  16       </p></li><li><p>
  17         Array nothrow <code class="function">new</code>, returning
  18         <code class="constant">NULL</code> on errors
  19       </p></li><li><p>
  20         Placement <code class="function">new</code>, which does nothing (like
  21         it's supposed to)
  22       </p></li><li><p>
  23         Placement array <code class="function">new</code>, which also does
  24         nothing
  25       </p></li></ul></div><p>
  26      They are distinguished by the parameters that you pass to them, like
  27      any other overloaded function.  The six flavors of <code class="function">delete</code>
  28      are distinguished the same way, but none of them are allowed to throw
  29      an exception under any circumstances anyhow.  (They match up for
  30      completeness' sake.)
  31    </p><p>
  32      Remember that it is perfectly okay to call <code class="function">delete</code> on a
  33      NULL pointer!  Nothing happens, by definition.  That is not the
  34      same thing as deleting a pointer twice.
  35    </p><p>
  36      By default, if one of the “<span class="quote">throwing <code class="function">new</code>s</span>” can't
  37      allocate the memory requested, it tosses an instance of a
  38      <code class="classname">bad_alloc</code> exception (or, technically, some class derived
  39      from it).  You can change this by writing your own function (called a
  40      new-handler) and then registering it with <code class="function">set_new_handler()</code>:
  41    </p><pre class="programlisting">
  42    typedef void (*PFV)(void);
  43
  44    static char*  safety;
  45    static PFV    old_handler;
  46
  47    void my_new_handler ()
  48    {
  49        delete[] safety;
  50        popup_window ("Dude, you are running low on heap memory.  You
  51                       should, like, close some windows, or something.
  52                       The next time you run out, we're gonna burn!");
  53        set_new_handler (old_handler);
  54        return;
  55    }
  56
  57    int main ()
  58    {
  59        safety = new char[500000];
  60        old_handler = set_new_handler (&amp;my_new_handler);
  61        ...
  62    }
  63    </pre><p>
  64      <code class="classname">bad_alloc</code> is derived from the base <code class="classname">exception</code>
  65      class defined in Chapter 19.
  66    </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk01pt02ch04s03.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="bk01pt02ch06.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">NULL </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 6. Termination</td></tr></table></div></body></html>