Re: How to make this exception-safe

From:

Ulrich Eckhardt <eckhardt@satorlaser.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Wed, 19 Nov 2008 15:25:40 CST

Message-ID:

<o91dv5-31p.ln1@satorlaser.homedns.org>

Triple-DES 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) );
   }

Use vector's reserve() function. Alternatively, use a temporary auto_ptr:

  auto_ptr<C> p(new C(2));
  v_.push_back(p.get());
  p.release();

Note that you must not use the returnvalue of p.release(), because then you
first release ownership while the vector is reallocated. That said, this
still won't work, because the destructor of V will not be called when the
constructor throws, but the destructor of vector<> will not delete the
elements it points to. Therefore: try, catch, rethrow.

Uli

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