Re: How to make this exception-safe
On Nov 18, 8:43 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?
PS! boost/tr1 shared_ptr or similar can not be used.
Why not? (It's important to know what constraints we are working
under.)
I would suggest using a container which holds pointers and manages
lifetimes -- boost has a few under the name Pointer Container.
Otherwise:
namespace
{
std::auto_ptr<C> new_C(int n) { return std::auto_ptr<C>(n); }
}
V::V() {
std::auto_ptr<C> a[] = {
new_C(2),
new_C(1),
new_C(3)
};
const size_t count = sizeof a / sizeof a[0]
v_.reserve(count);
std::transform(a, a + count, std::back_inserter(v_),
boost::bind(&std::auto_ptr<C>::release, _1));
}
Or, of course:
V::V() {
v_.reserve(3);
try {
v_.push_back( new C(2) );
v_.push_back( new C(1) );
v_.push_back( new C(3) );
}
catch (...) {
<call cleanup function>
throw;
}
}
Yechezkel Mett
--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]