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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. |
| 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> |
| 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" style="list-style-type: disc; "><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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