Re: How to make this exception-safe

On Nov 18, 10:43 am, Triple-DES <DenPlettf...@gmail.com> wrote:


This is overly verbose. You could do it just with

#include <memory>
V::V() {
    v_.reserve(3);
    v_.push_back( new C(2) );
    v_.push_back( new C(1) );
    v_.push_back( new C(3) );
}

The auto_ptrs in the quoted example do nothing to make your code more
exception safe. It does not address the basic problem. The basic
problem is for:
    vec.push_back(new foo());
and
    vec.push_back(some_auto_ptr.release());
the "new foo()" or "release()" may complete successfully, but then
push_back will fail with an exception, and then the pointer will be
lost and we will have a leak. The reserve call fixes this by
guaranteeing that the next push_backs will not fail or throw.

In such situations where I find myself storing dynamically allocated
objects by pointer into vectors, I write code like:

vec.push_back(0);
vec.back() = new foo();

If the vector is on the stack, I have previously defined ON_BLOCK_EXIT
or some sort of stack object whose destructor will free the contents,
so no leaks here. If the vector is a class member, then the class
destructor will delete the contents, so no leaks in that case either.
It works.

I would hazard a guess that the more elegant way is to use a class
template like std::vector which has ownership of the pointers like
std::auto_ptr.

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