6.9 Java Exceptions

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:

struct S { ~S(); }; extern void bar(); // is implemented 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 for the Java exception model, or vice versa, but there may be bugs in this area.