Re: How to make this exception-safe

Maxim Yegorushkin <>
Wed, 19 Nov 2008 15:25:45 CST
On Nov 18, 6:43 pm, Triple-DES <> wrote:

Consider the following code:

#include <vector>

struct C {
   explicit C(int) {} // may throw
     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

   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() {

   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

        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;

            : 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;


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