<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>Smart Pointer Changes</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> </head> <body bgcolor="#ffffff" text="#000000"> <h1><A href="../../index.htm"><img src="../../boost.png" alt="boost.png (6897 bytes)" align="middle" width="277" height="86" border="0"></A>Smart Pointer Changes</h1> <p>The February 2002 change to the Boost smart pointers introduced a number of changes. Since the previous version of the smart pointers was in use for a long time, it's useful to have a detailed list of what changed from a library user's point of view.</p> <p>Note that for compilers that don't support member templates well enough, a separate implementation is used that lacks many of the new features and is more like the old version.</p> <h2>Features Requiring Code Changes to Take Advantage</h2> <ul> <li> The smart pointer class templates now each have their own header file. For compatibility, the <a href="../../boost/smart_ptr.hpp"><boost/smart_ptr.hpp></a> header now includes the headers for the four classic smart pointer class templates. <li> The <b>weak_ptr</b> template was added. <li> The new <b>shared_ptr</b> and <b>shared_array</b> relax the requirement that the pointed-to object's destructor must be visible when instantiating the <b>shared_ptr</b> destructor. This makes it easier to have shared_ptr members in classes without explicit destructors. <li> A custom deallocator can be passed in when creating a <b>shared_ptr</b> or <b>shared_array</b>. <li> <b>shared_static_cast</b> and <b>shared_dynamic_cast</b> function templates are provided which work for <b>shared_ptr</b> and <b>weak_ptr</b> as <b>static_cast</b> and <b>dynamic_cast</b> do for pointers. <li> The self-assignment misfeature has been removed from <b>shared_ptr::reset</b>, although it is still present in <b>scoped_ptr</b>, and in <b>std::auto_ptr</b>. Calling <b>reset</b> with a pointer to the object that's already owned by the <b>shared_ptr</b> results in undefined behavior (an assertion, or eventually a double-delete if assertions are off). <li> The <b>BOOST_SMART_PTR_CONVERSION</b> feature has been removed. <li> <b>shared_ptr<void></b> is now allowed.</li> </ul> <h2>Features That Improve Robustness</h2> <ul> <li> The manipulation of use counts is now <a name="threadsafe">thread safe</a> on Windows, Linux, and platforms that support pthreads. See the <a href="../../boost/detail/atomic_count.hpp"> <boost/detail/atomic_count.hpp></a> file for details <li> The new shared_ptr will always delete the object using the pointer it was originally constructed with. This prevents subtle problems that could happen if the last <b>shared_ptr</b> was a pointer to a sub-object of a class that did not have a virtual destructor.</li> </ul> <h2>Implementation Details</h2> <ul> <li> Some bugs in the assignment operator implementations and in <b>reset</b> have been fixed by using the "copy and swap" idiom. <li> Assertions have been added to check preconditions of various functions; however, since these use the new <a href="../../boost/assert.hpp"><boost/assert.hpp></a> header, the assertions are disabled by default. <li> The partial specialization of <b>std::less</b> has been replaced by <b>operator<</b> overloads which accomplish the same thing without relying on undefined behavior. <li> The incorrect overload of <b>std::swap</b> has been replaced by <b>boost::swap</b>, which has many of the same advantages for generic programming but does not violate the C++ standard.</li> </ul> <hr> <p>Revised 1 February 2002</p> <p><small>Copyright 2002 Darin Adler. Distributed under the Boost Software License, Version 1.0. See accompanying file <A href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</A> or copy at <A href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>.</small></p> </body> </html>
