[Voted into the WP at the November, 2010 meeting.]

Proposed resolution (August, 2010):

1. Change 14.6.2 [except.terminate] paragraph 1 as follows:

In the following some situations exception handling must be abandoned for less subtle error handling techniques:. [Note: These situations are:

• when the exception handling mechanism, after completing evaluation of the expression to be thrown but before the exception is caught (14.2 [except.throw]), calls a function that exits via an uncaught exception, [Footnote: For example, if the object being thrown is of a class with a copy constructor, std::terminate() will be called if that copy constructor exits with an exception during a throw. —end footnote] or

• when the exception handling mechanism cannot find a handler for a thrown exception (14.4 [except.handle]), or

• when the search for a handler (14.4 [except.handle]) encounters the outermost block of a function with a noexcept-specification that does not allow the exception (14.5 [except.spec]), or

• when the destruction of an object during stack unwinding (15.2) terminates by throwing an exception, or

• when initialization of a non-local variable with static or thread storage duration (6.10.3.2 [basic.start.static], 6.10.3.3 [basic.start.dynamic]) terminates by throwing exits via an exception, or

• when destruction of an object with static or thread storage duration exits using via an exception (6.10.3.3 [basic.start.dynamic]), or

• when execution of a function registered with std::atexit or std::at_quick_exit exits using via an exception (17.5 [support.start.term]), or

• when a throw-expression with no operand attempts to rethrow an exception and no exception is being handled (14.2 [except.throw]), or

• when std::unexpected throws an exception which is not allowed by the previously violated dynamic-exception-specification, and std::bad_exception is not included in that dynamic-exception-specification (_N4606_.15.5.2 [except.unexpected]), or

• when the implementation's default unexpected exception handler is called (_N4606_.D.6.1 [unexpected.handler])., or

• when the function std::nested_exception::rethrow_nested is called for an object that has captured no exception (17.9.8 [except.nested]), or

• when execution of the initial function of a thread exits via an exception (32.4.3.4 [thread.thread.constr]), or

• when the destructor or the copy assignment operator is invoked on a std::thread object that refers to a joinable thread (32.4.3.5 [thread.thread.destr], 32.4.3.6 [thread.thread.assign]).

—end note]

2. Insert the following as a new paragraph following 14.2 [except.throw] paragraph 6:

An exception is considered caught...

If the exception handling mechanism, after completing evaluation of the expression to be thrown but before the exception is caught, calls a function that exits via an exception, std::terminate is called (14.6.2 [except.terminate]). [Example:

    struct C {
      C() { }
      C(const C&) { throw 0; }
    };
    int main() {
      try {
        throw C();   // calls std::terminate()
      } catch(C) { }
    }

—end example]

3. Change 14.3 [except.ctor] paragraph 3 as follows:

The process of calling destructors for automatic objects constructed on the path from a try block to a throw-expression is called “stack unwinding.” [Note: If a destructor called during stack unwinding exits with an exception, std::terminate is called (14.6.2 [except.terminate]). [Note: So destructors should generally catch exceptions and not let them propagate out of the destructor. —end note]

4. Change 6.10.3.2 [basic.start.static] paragraph 6 as follows:

[Note: If the initialization of a non-local variable with static or thread storage duration terminates by throwing exits via an exception, std::terminate is called (see 14.6.2 [except.terminate]). —end note]

5. Change 6.10.3.3 [basic.start.dynamic] paragraph 1 as follows:

...[Note: If the destruction of a non-local an object with static or thread storage duration terminates by throwing exits via an exception, std::terminate is called (see 14.6.2 [except.terminate]). —end note]

6. Change 17.5 [support.start.term] bullet 8.1 as follows:

• First, objects with thread storage duration...

  If control leaves a registered function called by exit because the function does not provide a handler for a thrown exception, terminate() shall be called (14.6.2 [except.terminate]).

N3092 comment GB 47

The list of reasons for which std::terminate is called needs to be extended to cover several additional cases in C++0x:

• when function std::nested_exception::rethrow_nested is called for an object that stores a null exception pointer.

• when execution of a function registered with std::at_quick_exit exits using an exception.

• when the destructor or a copy constructor of class std::thread is called for the object that is joinable.