Re: Smart Pointers and Microsoft Foundation Classes

From:
"Roger Rabbit" <roger@rabbit.com>
Newsgroups:
microsoft.public.vc.mfc
Date:
Tue, 19 Feb 2008 17:13:19 -0800
Message-ID:
<8075D0D1-ACDE-41EA-8686-94FB3B6ED877@microsoft.com>
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Here is my latest code snippet to act as a LockProxy for 'repairing' a =
bad design of my counted reference pointer program I wrote late last =
night . So I am considering it legacy code just to find out how abstract =
I can get C++ to go.....

#include <msclr/lock.h> // compile with /clr for the Windows calls
using namespace System;
using namespace System::Threading;
using namespace msclr;
//The proxy for fixing the legacy application code to minimize changes
template <class T>
ref class LockProxy {
public:
LockProxy(T* pObj) : pointee (pObj) { lock l(this); }
~LockProxy() { lock l(this); }
LockProxy operator->() const { return pointee; }
LockProxy operator&() const { return pointee&; }
LockProxy operator++() const {
lock l(this); // lock on an increment
return pointee++;
}
LockProxy operator--() const {
lock l(this); // lock on an decrement
return pointee--;
}
bool operator==(LockProxy(T)) const {
return this==pointee;
}
bool operator<(LockProxy(T)) const {
return this<pointee;
}
private:
T* pointee;
};

"Doug Harrison [MVP]" <dsh@mvps.org> wrote in message =
news:k28mr3he6h148ev9ogvtkcg2a7kdvafrog@4ax.com...

On Tue, 19 Feb 2008 10:19:41 -0800, "Roger Rabbit" <roger@rrabbit.com>
wrote:
 

Consider this, when I write win_main(...)I create a handle to my =

instance

that is running. I could use the pointer to determine if I am running =

a

second instance or not. I could for example see that I am already =

running,

so what not spawn a new tab in the document window.

 
Sure, you could write a class to manage that. I wouldn't call it a =

"smart

pointer", though, because that's really stretching the meaning of the =

term.

In C++, the term is used to describe a class that solves some of the
problems that come with raw pointers, such as the need to delete them =

at

some point.
 

For example a multi document interface text editor would create an =

abstract

Document and derive TextDocument and RichTextDocument classes. That =

seems

pretty basic, but its more tricky when a new tab surfaces. Ownership =

becomes

important which is why I started pondering smart pointers in the first =

place.

 
Ownership is always important. Smart pointers can help you implement =

the

ownership semantics you require.
 
--
Doug Harrison
Visual C++ MVP

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; =
charset=unicode">
<META content="MSHTML 6.00.6000.16587" name=GENERATOR></HEAD>
<BODY id=MailContainerBody
style="PADDING-RIGHT: 10px; PADDING-LEFT: 10px; PADDING-TOP: 15px"
bgColor=#ffffff leftMargin=0 topMargin=0 CanvasTabStop="true"
name="Compose message area"><FONT size=4>Here is my latest code =
snippet to act
as a LockProxy for 'repairing' a bad design of my counted reference =
pointer
program I wrote late last night . So I am considering it legacy code =
just to
find out how abstract I can get C++ to go.....<BR><BR></FONT><FONT =
size=4><FONT
face="Courier New">#include =
&lt;msclr/lock.h&gt;&nbsp;&nbsp;&nbsp;&nbsp; //
compile with /clr for the Windows calls<BR>using namespace =
System;<BR>using
namespace System::Threading;<BR>using namespace msclr;<BR>//The proxy =
for fixing
the legacy application code to minimize changes<BR>template &lt;class
T&gt;<BR>ref class LockProxy {<BR>public:<BR>LockProxy(T* pObj) : =
pointee (pObj)
{ lock l(this); }<BR>~LockProxy() { lock l(this); }<BR>LockProxy =
operator-&gt;()
const { return pointee; }<BR>LockProxy operator&amp;() const { return
pointee&amp;; }<BR>LockProxy operator++() const {<BR>lock l(this); // =
lock on an
increment<BR>return pointee++;<BR>}<BR>LockProxy operator--() const =
{<BR>lock
l(this); // lock on an decrement<BR>return pointee--;<BR>}<BR>bool
operator==(LockProxy(T)) const {<BR>return =
this==pointee;<BR>}<BR>bool
operator&lt;(LockProxy(T)) const {<BR>return
this&lt;pointee;<BR>}<BR>private:<BR>T* =
pointee;<BR>};<BR></FONT><BR><BR>"Doug
Harrison [MVP]" &lt;dsh@mvps.org&gt; wrote in message
news:k28mr3he6h148ev9ogvtkcg2a7kdvafrog@4ax.com...<BR>&gt; On Tue, 19 =
Feb 2008
10:19:41 -0800, "Roger Rabbit" &lt;roger@rrabbit.com&gt;<BR>&gt; =
wrote:<BR>&gt;
<BR>&gt;&gt;Consider this, when I write win_main(...)I create a handle =
to my
instance <BR>&gt;&gt;that is running. I could use the pointer to =
determine if I
am running a <BR>&gt;&gt;second instance or not. I could for example see =
that I
am already running, <BR>&gt;&gt;so what not spawn a new tab in the =
document
window.<BR>&gt; <BR>&gt; Sure, you could write a class to manage that. I =

wouldn't call it a "smart<BR>&gt; pointer", though, because that's =
really
stretching the meaning of the term.<BR>&gt; In C++, the term is used to =
describe
a class that solves some of the<BR>&gt; problems that come with raw =
pointers,
such as the need to delete them at<BR>&gt; some point.<BR>&gt; =
<BR>&gt;&gt;For
example a multi document interface text editor would create an abstract
<BR>&gt;&gt;Document and derive TextDocument and RichTextDocument =
classes. That
seems <BR>&gt;&gt;pretty basic, but its more tricky when a new tab =
surfaces.
Ownership becomes <BR>&gt;&gt;important which is why I started pondering =
smart
pointers in the first <BR>&gt;&gt;place.<BR>&gt; <BR>&gt; Ownership is =
always
important. Smart pointers can help you implement the<BR>&gt; ownership =
semantics
you require.<BR>&gt; <BR>&gt; -- <BR>&gt; Doug Harrison<BR>&gt; Visual =
C++
MVP</FONT></BODY></HTML>

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