Re: How to make this exception-safe
On Nov 18, 6:43 pm, Triple-DES <DenPlettf...@gmail.com> wrote:
Consider the following code:
#include <vector>
struct C {
explicit C(int) {} // may throw
private:
C(const C&);
C& operator=(const C&);
};
struct V {
V() {
// may leak if push_back or C::C(int) throws
v_.push_back( new C(2) );
v_.push_back( new C(1) );
v_.push_back( new C(3) );
}
~V() {} // delete all elems of v
private:
std::vector<C*> v_;
};
How would you go about making an exception-safe version of V::V()?
This is what I could come up with:
// 1st attempt
#include <memory>
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() );
}
Which is tedious if you are inserting more objects. Does anyone have a
better solution?
One solution is to use a vector of smart pointers.
Another is to use an intrusive list if your container does not have to
be an array. Allocate nodes, once a node has been allocated inserting
it in a list never throws:
#include <memory>
struct C {
explicit C(int) {} // may throw
private:
C(const C&);
C& operator=(const C&);
};
struct NodeC : C
{
explicit NodeC(int x)
: C(x)
{}
std::auto_ptr<NodeC> next;
};
struct V
{
std::auto_ptr<NodeC> head, *tail;
V()
: tail(&head)
{
// if any of these throw, the destructor
// of head takes care of cleaning it up
*tail = new NodeC(1);
tail = &(**tail).next;
*tail = new NodeC(2);
tail = &(**tail).next;
*tail = new NodeC(3);
tail = &(**tail).next;
}
};
--
Max
--
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