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Add "use virtual inheritance" rule

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[SVN r19721]
This commit is contained in:
Dave Abrahams 2003-08-21 14:46:28 +00:00
parent 3994937575
commit d6774a7efc
1 changed files with 31 additions and 3 deletions
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34
error_handling.html
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@ -58,12 +58,40 @@
<h3>How should I design my exception classes?</h3>
<ol>
<li><b>Inherit from <code>std::exception</code></b>. Except in *very*
rare circumstances where you can't afford the cost of a virtual table,
<li><b>Derive your exception class
from <code>std::exception</code></b>. Except in *very* rare
circumstances where you can't afford the cost of a virtual
table,
<code>std::exception</code> makes a reasonable exception base class,
and when used universally, allows programmers to catch "everything"
without resorting to <code>catch(...)</code>. For more about
<code>catch(...)</code>, see below.</li>
<code>catch(...)</code>, see below.
<li><b>Use <i>virtual</i> inheritance.</b> This insight is due
to Andrew Koenig. Using virtual inheritance from your
exception's base class(es) prevents ambiguity problems at the
catch-site in case someone throws an exception derived from
multiple bases which have a base class in common:
<pre>
#include &lt;iostream&gt;
struct my_exc1 : std::exception { char const* what() throw(); };
struct my_exc2 : std::exception { char const* what() throw(); };
struct your_exc3 : my_exc1, my_exc2 {};
int main()
{
try { throw your_exc3(); }
catch(std::exception const&amp; e) {}
catch(...) { std::cout &lt;&lt; &quot;whoops!&quot; &lt;&lt; std::endl; }
}
</pre>
The program above prints <code>&quot;whoops&quot;</code> because the
C++ runtime can't resolve which <code>exception</code> instance to
match in the first catch clause.
</li>
<li>
<b><i>Don't</i> embed a std::string object</b> or any other data