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<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=" ISO C++ , library "/><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.
Support
</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>
There are six flavors each of <code class="function">new</code> and
<code class="function">delete</code>, so make certain that you're using the right
ones. Here are quickie descriptions of <code class="function">new</code>:
</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>
single object form, throwing a
<code class="classname">bad_alloc</code> on errors; this is what most
people are used to using
</p></li><li class="listitem"><p>
Single object "nothrow" form, returning NULL on errors
</p></li><li class="listitem"><p>
Array <code class="function">new</code>, throwing
<code class="classname">bad_alloc</code> on errors
</p></li><li class="listitem"><p>
Array nothrow <code class="function">new</code>, returning
<code class="constant">NULL</code> on errors
</p></li><li class="listitem"><p>
Placement <code class="function">new</code>, which does nothing (like
it's supposed to)
</p></li><li class="listitem"><p>
Placement array <code class="function">new</code>, which also does
nothing
</p></li></ul></div><p>
They are distinguished by the parameters that you pass to them, like
any other overloaded function. The six flavors of <code class="function">delete</code>
are distinguished the same way, but none of them are allowed to throw
an exception under any circumstances anyhow. (They match up for
completeness' sake.)
</p><p>
Remember that it is perfectly okay to call <code class="function">delete</code> on a
NULL pointer! Nothing happens, by definition. That is not the
same thing as deleting a pointer twice.
</p><p>
By default, if one of the <span class="quote">“<span class="quote">throwing <code class="function">new</code>s</span>”</span> can't
allocate the memory requested, it tosses an instance of a
<code class="classname">bad_alloc</code> exception (or, technically, some class derived
from it). You can change this by writing your own function (called a
new-handler) and then registering it with <code class="function">set_new_handler()</code>:
</p><pre class="programlisting">
typedef void (*PFV)(void);
static char* safety;
static PFV old_handler;
void my_new_handler ()
{
delete[] safety;
popup_window ("Dude, you are running low on heap memory. You
should, like, close some windows, or something.
The next time you run out, we're gonna burn!");
set_new_handler (old_handler);
return;
}
int main ()
{
safety = new char[500000];
old_handler = set_new_handler (&my_new_handler);
...
}
</pre><p>
<code class="classname">bad_alloc</code> is derived from the base <code class="classname">exception</code>
class defined in Sect1 19.
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