boost_mirror/utility
1
0
Fork 0
mirror of https://github.com/boostorg/utility.git synced 2025-05-09 15:04:00 +00:00
Code Issues Packages Projects Releases Wiki Activity

checked_delete.hpp documentation added.

Browse Source 
[SVN r16238]
This commit is contained in:
Peter Dimov 2002-11-14 14:53:32 +00:00
parent 2b7d10aceb
commit 32fb45eba9
4 changed files with 267 additions and 197 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

124
checked_delete.html Normal file
View File

@ -0,0 +1,124 @@
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>Boost: checked_delete.hpp documentation</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
</head>
<body bgcolor="white" style="MARGIN-LEFT: 5%; MARGIN-RIGHT: 5%">
<table border="0" width="100%">
<tr>
<td width="277">
<img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" width="277" height="86">
</td>
<td align="middle">
<h1>checked_delete.hpp</h1>
</td>
</tr>
<tr>
<td colspan="2" height="64">&nbsp;</td>
</tr>
</table>
<p>
The header <STRONG>&lt;boost/checked_delete.hpp&gt;</STRONG> defines two
function templates, <STRONG>checked_delete</STRONG> and <STRONG>checked_array_delete</STRONG>,
and two class templates, <STRONG>checked_deleter</STRONG> and <STRONG>checked_array_deleter</STRONG>.
</p>
<P>The C++ Standard allows, in 5.3.5/5, pointers to incomplete class types to
be deleted with a <EM>delete-expression</EM>. When the class has a non-trivial
destructor, or a class-specific operator delete, the behavior is undefined.
Some compilers issue a warning when an incomplete type is deleted, but
unfortunately, not all do, and programmers sometimes ignore or disable
warnings.</P>
<P>A particularly troublesome case is when a smart pointer's destructor, such as <STRONG>
boost::scoped_ptr&lt;T&gt;::~scoped_ptr</STRONG>, is instantiated with an
incomplete type. This can often lead to silent, hard to track failures.</P>
<P>The supplied function and class templates can be used to prevent these problems,
as they require a complete type, and cause a compilation error otherwise.</P>
<h3><a name="Synopsis">Synopsis</a></h3>
<pre>
namespace boost
{
template&lt;class T&gt; void checked_delete(T * p);
template&lt;class T&gt; void checked_array_delete(T * p);
template&lt;class T&gt; struct checked_deleter;
template&lt;class T&gt; struct checked_array_deleter;
}
</pre>
<h3>checked_delete</h3>
<h4><a name="checked_delete">template&lt;class T&gt; void checked_delete(T * p);</a></h4>
<blockquote>
<p>
<b>Requires:</b> <b>T</b> must be a complete type. The expression <tt>delete p</tt>
must be well-formed.
</p>
<p>
<b>Effects:</b> <tt>delete p;</tt>
</p>
</blockquote>
<h3>checked_array_delete</h3>
<h4><a name="checked_array_delete">template&lt;class T&gt; void checked_array_delete(T
* p);</a></h4>
<blockquote>
<p>
<b>Requires:</b> <b>T</b> must be a complete type. The expression <tt>delete [] p</tt>
must be well-formed.
</p>
<p>
<b>Effects:</b> <tt>delete [] p;</tt>
</p>
</blockquote>
<h3>checked_deleter</h3>
<pre>
template&lt;class T&gt; struct checked_deleter
{
typedef void result_type;
typedef T * argument_type;
void operator()(T * p);
};
</pre>
<h4>void checked_deleter&lt;T&gt;::operator()(T * p);</h4>
<blockquote>
<p>
<b>Requires:</b> <b>T</b> must be a complete type. The expression <tt>delete p</tt>
must be well-formed.
</p>
<p>
<b>Effects:</b> <tt>delete p;</tt>
</p>
</blockquote>
<h3>checked_array_deleter</h3>
<pre>
template&lt;class T&gt; struct checked_array_deleter
{
typedef void result_type;
typedef T * argument_type;
void operator()(T * p);
};
</pre>
<h4>void checked_array_deleter&lt;T&gt;::operator()(T * p);</h4>
<blockquote>
<p>
<b>Requires:</b> <b>T</b> must be a complete type. The expression <tt>delete [] p</tt>
must be well-formed.
</p>
<p>
<b>Effects:</b> <tt>delete [] p;</tt>
</p>
</blockquote>
<h3><a name="Acknowledgements">Acknowledgements</a></h3>
<p>
The function templates <STRONG>checked_delete</STRONG> and <STRONG>checked_array_delete</STRONG>
were originally part of <STRONG>&lt;boost/utility.hpp&gt;</STRONG>, and the
documentation acknowledged Beman Dawes, Dave Abrahams, Vladimir Prus,
Rainer Deyke, John Maddock, and others as contributors.
</p>
<p>
<br>
<small>Copyright © 2002 by Peter Dimov. Permission to copy, use, modify, sell
and distribute this document is granted provided this copyright notice appears
in all copies. This document is provided "as is" without express or implied
warranty, and with no claim as to its suitability for any purpose.</small></p>
</body>
</html>

3
include/boost/checked_delete.hpp
View File

@ -9,12 +9,15 @@
// boost/checked_delete.hpp
//
// Copyright (c) 1999, 2000, 2001, 2002 boost.org
// Copyright (c) 2002 Peter Dimov
//
// Permission to copy, use, modify, sell and distribute this software
// is granted provided this copyright notice appears in all copies.
// This software is provided "as is" without express or implied
// warranty, and with no claim as to its suitability for any purpose.
//
// http://www.boost.org/libs/utility/checked_delete.html
//
namespace boost
{

49
index.html
View File

@ -1,34 +1,31 @@
<html>
<head>
<meta http-equiv="Content-Language" content="en-us">
<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
<meta name="ProgId" content="FrontPage.Editor.Document">
<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<title>Boost Utility Library</title>
</head>
<body bgcolor="#FFFFFF">
<h1><IMG SRC="../../c++boost.gif" WIDTH="276" HEIGHT="86" align="center">Boost
Utility Library</h1>
<p>The Boost Utility Library isn't really a single library at all.&nbsp; It is
just a collection for components too small to be called libraries in their own
right.</p>
<p>But that doesn't mean there isn't useful stuff here.&nbsp; Take a look:</p>
<blockquote>
<head>
<meta http-equiv="Content-Language" content="en-us">
<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
<meta name="ProgId" content="FrontPage.Editor.Document">
<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<title>Boost Utility Library</title>
</head>
<body bgcolor="#FFFFFF">
<h1><IMG SRC="../../c++boost.gif" WIDTH="276" HEIGHT="86" align="center">Boost
Utility Library</h1>
<p>The Boost Utility Library isn't really a single library at all. It is just
a collection for components too small to be called libraries in their own
right.</p>
<p>But that doesn't mean there isn't useful stuff here. Take a look:</p>
<blockquote>
<p><a href="base_from_member.html">base_from_member</a><br>
<a href="call_traits.htm">call_traits.htm</a><br>
<a href="checked_delete.html">checked_delete.html</a><br>
<a href="compressed_pair.htm">compressed_pair.htm</a><br>
<a href="operators.htm">operators.htm</a><br>
<a href="tie.html">tie</a><br>
<a href="utility.htm">utility.htm</a></p>
</blockquote>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->07 May, 2002<!--webbot bot="Timestamp" endspan i-checksum="13976" --></p>
<p>&nbsp;</p>
</body>
</blockquote>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
07 May, 2002<!--webbot bot="Timestamp" endspan i-checksum="13976" --></p>
<p>&nbsp;</p>
</body>
</html>

268
utility.htm
View File

@ -1,168 +1,114 @@
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Header boost/utility.hpp Documentation</title>
</head>
<body bgcolor="#FFFFFF" text="#000000">
<h1><img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" align="center" WIDTH="277" HEIGHT="86">Header
<a href="../../boost/utility.hpp">boost/utility.hpp</a></h1>
<p>The entire contents of the header <code><a href="../../boost/utility.hpp">&lt;boost/utility.hpp&gt;</a></code>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Header boost/utility.hpp Documentation</title>
</head>
<body bgcolor="#FFFFFF" text="#000000">
<h1><img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" align="center" WIDTH="277" HEIGHT="86">Header
<a href="../../boost/utility.hpp">boost/utility.hpp</a></h1>
<p>The entire contents of the header <code><a href="../../boost/utility.hpp">&lt;boost/utility.hpp&gt;</a></code>
are in <code>namespace boost</code>.</p>
<h2>Contents</h2>
<ul>
<li>Class templates supporting the <a href="base_from_member.html">base-from-member
<h2>Contents</h2>
<ul>
<li>
Class templates supporting the <a href="base_from_member.html">base-from-member
idiom</a></li>
<li>Function templates <a href="#checked_delete">checked_delete() and
<li>
Function templates <a href="#checked_delete">checked_delete() and
checked_array_delete()</a></li>
<li>Function templates <a href="#functions next">next() and prior()</a></li>
<li>Class <a href="#Class noncopyable">noncopyable</a></li>
<li>Function template <a href="#addressof">addressof()</a></li>
<li>Function template <a href="tie.html">tie()</a> and supporting class tied.</li>
</ul>
<h2> Function templates <a name="checked_delete">checked_delete</a>() and
checked_array_delete()</h2>
<p>Deletion of a pointer to an incomplete type is an unsafe programming practice
because there is no way for the compiler to verify that the destructor is indeed
trivial.&nbsp; The checked_delete() and checked_array_delete() function
templates simply <b>delete</b> or <b>delete[]</b> their argument, but also
require that their argument be a complete type.&nbsp; They issue an appropriate
compiler error diagnostic if that requirement is not met.&nbsp; A typical
implementation is shown; other implementations may vary:</p>
<pre> template&lt; typename T &gt;
inline void checked_delete(T const volatile * x)
{
BOOST_STATIC_ASSERT( sizeof(T) ); // assert type complete at point
// of instantiation
delete x;
}
template&lt; typename T &gt;
inline void checked_array_delete(T const volatile * x)
{
BOOST_STATIC_ASSERT( sizeof(T) ); // assert type complete at point
// of instantiation
delete [] x;
}</pre>
<p>Contributed by Beman Dawes, based on a suggestion from Dave Abrahams,
generalizing an idea from Vladimir Prus, with comments from Rainer Deyke, John
Maddock, and others.</p>
<h3>Background</h3>
<p>The C++ Standard specifies that delete on a pointer to an incomplete types is
undefined behavior if the type has a non-trivial destructor in&nbsp; [expr.delete]
5.3.5 paragraph.&nbsp; No diagnostic is required.&nbsp; Some but not all
compilers issue warnings if the type is incomplete at point of deletion.</p>
<h2> <a name="functions next">Function</a> templates next() and prior()</h2>
<p>Certain data types, such as the C++ Standard Library's forward and
bidirectional iterators, do not provide addition and subtraction via operator+()
or operator-().&nbsp; This means that non-modifying computation of the next or
prior value requires a temporary, even though operator++() or operator--() is
provided.&nbsp; It also means that writing code like <code>itr+1</code> inside a
template restricts the iterator category to random access iterators.</p>
<p>The next() and prior() functions provide a simple way around these problems:</p>
<blockquote>
<pre>template &lt;class T&gt;
<li>
Function templates <a href="#functions next">next() and prior()</a></li>
<li>
Class <a href="#Class noncopyable">noncopyable</a></li>
<li>
Function template <a href="#addressof">addressof()</a></li>
<li>
Function template <a href="tie.html">tie()</a> and supporting class tied.</li>
</ul>
<h2>
Function templates <a name="checked_delete">checked_delete</a>() and
checked_array_delete()</h2>
<p>See <a href="checked_delete.html">separate documentation</a>.</p>
<h2>
<a name="functions next">Function</a> templates next() and prior()</h2>
<p>Certain data types, such as the C++ Standard Library's forward and bidirectional
iterators, do not provide addition and subtraction via operator+() or
operator-().&nbsp; This means that non-modifying computation of the next or
prior value requires a temporary, even though operator++() or operator--() is
provided.&nbsp; It also means that writing code like <code>itr+1</code> inside
a template restricts the iterator category to random access iterators.</p>
<p>The next() and prior() functions provide a simple way around these problems:</p>
<blockquote>
<pre>template &lt;class T&gt;
T next(T x) { return ++x; }
template &lt;class X&gt;
T prior(T x) { return --x; }</pre>
</blockquote>
<p>Usage is simple:</p>
<blockquote>
<pre>const std::list&lt;T&gt;::iterator p = get_some_iterator();
</blockquote>
<p>Usage is simple:</p>
<blockquote>
<pre>const std::list&lt;T&gt;::iterator p = get_some_iterator();
const std::list&lt;T&gt;::iterator prev = boost::prior(p);</pre>
</blockquote>
<p>Contributed by <a href="../../people/dave_abrahams.htm">Dave Abrahams</a>.</p>
<h2><a name="Class noncopyable">Class noncopyable</a></h2>
<p>Class <strong>noncopyable</strong> is a base class.&nbsp; Derive your own class from <strong>noncopyable</strong>
when you want to prohibit copy construction and copy assignment.</p>
<p>Some objects, particularly those which hold complex resources like files or
network connections, have no sensible copy semantics.&nbsp; Sometimes there are
possible copy semantics, but these would be of very limited usefulness and be
very difficult to implement correctly.&nbsp; Sometimes you're implementing a class that doesn't need to be copied
just yet and you don't want to take the time to write the appropriate functions.&nbsp;
Deriving from <b> noncopyable</b> will prevent the otherwise implicitly-generated
functions (which don't have the proper semantics) from becoming a trap for other programmers.</p>
<p>The traditional way to deal with these is to declare a private copy constructor and copy assignment, and then
document why this is done.&nbsp; But deriving from <b>noncopyable</b> is simpler
and clearer, and doesn't require additional documentation.</p>
<p>The program <a href="noncopyable_test.cpp">noncopyable_test.cpp</a> can be
used to verify class <b>noncopyable</b> works as expected. It has have been run successfully under
GCC 2.95, Metrowerks
CodeWarrior 5.0, and Microsoft Visual C++ 6.0 sp 3.</p>
<p>Contributed by <a href="../../people/dave_abrahams.htm">Dave Abrahams</a>.</p>
<h3>Example</h3>
<blockquote>
</blockquote>
<p>Contributed by <a href="../../people/dave_abrahams.htm">Dave Abrahams</a>.</p>
<h2><a name="Class noncopyable">Class noncopyable</a></h2>
<p>Class <strong>noncopyable</strong> is a base class.&nbsp; Derive your own class
from <strong>noncopyable</strong> when you want to prohibit copy construction
and copy assignment.</p>
<p>Some objects, particularly those which hold complex resources like files or
network connections, have no sensible copy semantics.&nbsp; Sometimes there are
possible copy semantics, but these would be of very limited usefulness and be
very difficult to implement correctly.&nbsp; Sometimes you're implementing a
class that doesn't need to be copied just yet and you don't want to take the
time to write the appropriate functions.&nbsp; Deriving from <b>noncopyable</b>
will prevent the otherwise implicitly-generated functions (which don't have the
proper semantics) from becoming a trap for other programmers.</p>
<p>The traditional way to deal with these is to declare a private copy constructor
and copy assignment, and then document why this is done.&nbsp; But deriving
from <b>noncopyable</b> is simpler and clearer, and doesn't require additional
documentation.</p>
<p>The program <a href="noncopyable_test.cpp">noncopyable_test.cpp</a> can be used
to verify class <b>noncopyable</b> works as expected. It has have been run
successfully under GCC 2.95, Metrowerks CodeWarrior 5.0, and Microsoft Visual
C++ 6.0 sp 3.</p>
<p>Contributed by <a href="../../people/dave_abrahams.htm">Dave Abrahams</a>.</p>
<h3>Example</h3>
<blockquote>
<pre>// inside one of your own headers ...
#include &lt;boost/utility.hpp&gt;
class ResourceLadenFileSystem : boost::noncopyable {
...</pre>
</blockquote>
<h3>Rationale</h3>
<p>Class noncopyable has protected constructor and destructor members to
emphasize that it is to be used only as a base class.&nbsp; Dave Abrahams notes
concern about the effect on compiler optimization of adding (even trivial inline)
destructor declarations. He says &quot;Probably this concern is misplaced, because
noncopyable will be used mostly for classes which own resources and thus have non-trivial destruction semantics.&quot;</p>
<h2><a name="addressof">Function template addressof()</a></h2>
<p>Function <strong>addressof()</strong> returns the address of an object.</p>
<blockquote>
<pre>
</blockquote>
<h3>Rationale</h3>
<p>Class noncopyable has protected constructor and destructor members to emphasize
that it is to be used only as a base class.&nbsp; Dave Abrahams notes concern
about the effect on compiler optimization of adding (even trivial inline)
destructor declarations. He says &quot;Probably this concern is misplaced,
because noncopyable will be used mostly for classes which own resources and
thus have non-trivial destruction semantics.&quot;</p>
<h2><a name="addressof">Function template addressof()</a></h2>
<p>Function <strong>addressof()</strong> returns the address of an object.</p>
<blockquote>
<pre>
template &lt;typename T&gt; inline T* addressof(T& v);
template &lt;typename T&gt; inline const T* addressof(const T& v);
template &lt;typename T&gt; inline volatile T* addressof(volatile T& v);
template &lt;typename T&gt; inline const volatile T* addressof(const volatile T& v);
</pre>
</blockquote>
<p>C++ allows programmers to replace the unary
<strong>operator&()</strong> class member used to get the address of
an object. Getting the real address of an object requires ugly
casting tricks to avoid invoking the overloaded
<strong>operator&()</strong>. Function <strong>addressof()</strong>
provides a wrapper around the necessary code to make it easy to get an
object's real address.
</p>
<p>The program <a href="addressof_test.cpp">addressof_test.cpp</a> can be
used to verify that <b>addressof()</b> works as expected.</p>
<p>Contributed by Brad King based on ideas from discussion with Doug Gregor.</p>
<h3>Example</h3>
<blockquote>
<pre>#include &lt;boost/utility.hpp&gt;
</blockquote>
<p>C++ allows programmers to replace the unary <strong>operator&()</strong> class
member used to get the address of an object. Getting the real address of an
object requires ugly casting tricks to avoid invoking the overloaded <strong>operator&()</strong>.
Function <strong>addressof()</strong> provides a wrapper around the necessary
code to make it easy to get an object's real address.
</p>
<p>The program <a href="addressof_test.cpp">addressof_test.cpp</a> can be used to
verify that <b>addressof()</b> works as expected.</p>
<p>Contributed by Brad King based on ideas from discussion with Doug Gregor.</p>
<h3>Example</h3>
<blockquote>
<pre>#include &lt;boost/utility.hpp&gt;
struct useless_type {};
class nonaddressable {
@ -174,20 +120,20 @@ void f() {
nonaddressable* xp = boost::addressof(x);
// nonaddressable* xpe = &amp;x; /* error */
}</pre>
</blockquote>
<h2>Class templates for the Base-from-Member Idiom</h2>
<p>See <a href="base_from_member.html">separate documentation</a>.</p>
<h2>Function template tie()</h2>
<p>See <a href="tie.html">separate documentation</a>.</p>
<hr>
<p>Revised&nbsp; <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan
-->10 September, 2001<!--webbot bot="Timestamp" endspan i-checksum="39328"
</blockquote>
<h2>Class templates for the Base-from-Member Idiom</h2>
<p>See <a href="base_from_member.html">separate documentation</a>.</p>
<h2>Function template tie()</h2>
<p>See <a href="tie.html">separate documentation</a>.</p>
<hr>
<p>Revised&nbsp; <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan
-->
</p>
<p>© Copyright boost.org 1999. Permission to copy, use, modify, sell and
distribute this document is granted provided this copyright notice appears in
all copies. This document is provided &quot;as is&quot; without express or
implied warranty, and with no claim as to its suitability for any purpose.</p>
</body>
10 September, 2001<!--webbot bot="Timestamp" endspan i-checksum="39328"
-->
</p>
<p>© Copyright boost.org 1999-2002. Permission to copy, use, modify, sell and distribute
this document is granted provided this copyright notice appears in all copies.
This document is provided &quot;as is&quot; without express or implied
warranty, and with no claim as to its suitability for any purpose.</p>
</body>
</html>