Re: How to make this exception-safe

From:
Triple-DES <DenPlettfrie@gmail.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Thu, 20 Nov 2008 14:23:23 CST
Message-ID:
<28c00be7-d48a-4037-bfa2-8ab50d884065@k19g2000yqg.googlegroups.com>
On 19 Nov, 22:24, Boris Rasin <rasin.bo...@gmail.com> wrote:

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.


I don't think it will leak if C::C(int) throws, and if push_back
throws your proposed solution will leak as well.


push_back should not throw after the call to reserve. I have already
demonstrated that the initial solution may leak.

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