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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 ‘<samp><span class="samp">__gxx_personality_v0</span></samp>’. |
| |
| <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 |
| ‘<samp><span class="samp">#pragma GCC java_exceptions<!-- /@w --></span></samp>’ at the head of the file. This |
| ‘<samp><span class="samp">#pragma</span></samp>’ 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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