Re: std::auto_ptr as exception object

James Kanze <>
Mon, 28 Apr 2008 03:06:16 -0700 (PDT)
On Apr 28, 9:19 am, wrote:

I am using std::auto_ptr to try to keep ownership of resources
straight. However, I became aware that exception objects must
provide a copy constructor, which made me uncertain of the
soundness of throwing std::auto_ptrs...

It was explained to me that a possible problem case is:

try {
  throw std::auto_ptr<int>(new int(10));
} catch (std::auto_ptr<int> a)

If I understood correctly, the re-throw would use the original
exception object, which has lost ownership.
Is there a way to prevent catching by value?
Is catching by reference kosher?

It's the usual practice, since it takes polymorphism into

Are there other problems with throwing auto_ptrs?

Well, the copy constructor takes a non-const reference, so you
cannot copy a temporary. (In other words, your example
shouldn't compile---although I couldn't find a compiler which
rejects it.)

The usual practice would be to throw by value, and catch by
const reference:

    try {
        throw 10 ;
    } catch ( int const& err ) {
        throw ;

(Of course, you almost never throw int's. In practice, you'd
throw some specific class derived from std::exception.)

James Kanze (GABI Software)
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