Re: How to make this exception-safe
On Nov 18, 6:43 pm, Triple-DES <DenPlettf...@gmail.com> wrote:
How would you go about making an exception-safe version of V::V()?
This is what I could come up with: [...]
V::V() {
v_.reserve(3);
std::auto_ptr<C> c1( new C(2) );
std::auto_ptr<C> c2( new C(1) );
std::auto_ptr<C> c3( new C(3) );
v_.push_back( c1.release() );
v_.push_back( c2.release() );
v_.push_back( c3.release() );
}
Why bother with the auto_ptrs? Once you have done the reserve, the
call to push_back is not permitted to cause a reallocation (assuming
you passed the right argument to reserve). The only other thing that
push_back does that might, in general, throw an exception is call the
copy constructor of the vector's value_type. However, in your code,
the value_type is C* -- a raw pointer -- and its copy constructor will
never throw. So you can simply write:
v_.reserve(3);
v_.push_back( new C(1) );
v_.push_back( new C(2) );
v_.push_back( new C(3) );
If the list of elements to be inserted is significantly longer than 3,
or if it's likely to be changed over time, I might do something like:
size_t const expected_size = 3;
v_.reserve(expected_size);
// ... call v_.push_back 3 times
assert( v_.size() == expected_size );
That way, if someone adds another push_back to the function, but
forgets to alter the reserve call, you will get an assertion failure
that will (hopefully!) be picked up during testing.
Richard Smith
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