7.12 Java Exceptions

The Java language uses a slightly different exception handling model from C++. Normally, GNU C++ automatically detects 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 guesses incorrectly. Sample problematic code is:

       struct S { ~S(); };
       extern void bar();    // is written in Java, and may throw exceptions

       void foo()
       {
         S s;
         bar();
       }

The usual effect of an incorrect guess is a link failure, complaining of a missing routine called ‘ __gxx_personality_v0 ’.

You can inform the compiler that Java exceptions are to be used in a translation unit, irrespective of what it might think, by writing ‘ #pragma GCC java_exceptions ’ at the head of the file. This ‘ #pragma ’ must appear before any functions that throw or catch exceptions, or run destructors when exceptions are thrown through them.

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.