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<h3 class="section">7.10 Java Exceptions</h3>

<p>The Java language uses a slightly different exception handling model
from C++.  Normally, GNU C++ will automatically detect when you are
writing C++ code that uses Java exceptions, and handle them
appropriately.  However, if C++ code only needs to execute destructors
when Java exceptions are thrown through it, GCC will guess incorrectly. 
Sample problematic code is:

<pre class="smallexample">       struct S { ~S(); };
       extern void bar();    // <span class="roman">is written in Java, and may throw exceptions</span>
       void foo()
       {
         S s;
         bar();
       }
</pre>
 <p class="noindent">The usual effect of an incorrect guess is a link failure, complaining of
a missing routine called &lsquo;<samp><span class="samp">__gxx_personality_v0</span></samp>&rsquo;.

 <p>You can inform the compiler that Java exceptions are to be used in a
translation unit, irrespective of what it might think, by writing
&lsquo;<samp><span class="samp">#pragma&nbsp;GCC&nbsp;java_exceptions<!-- /@w --></span></samp>&rsquo; at the head of the file.  This
&lsquo;<samp><span class="samp">#pragma</span></samp>&rsquo; must appear before any functions that throw or catch
exceptions, or run destructors when exceptions are thrown through them.

 <p>You cannot mix Java and C++ exceptions in the same translation unit.  It
is believed to be safe to throw a C++ exception from one file through
another file compiled for the Java exception model, or vice versa, but
there may be bugs in this area.

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