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I'm working around it by putting everything except the call to the overridden function in a new member function (Init). This way it works, but both constructors have the same code.
foo() {
init(); //foo::init()
bar(); //foo::bar()
}
fooplus() {
init(); //foo::init();
bar(); //fooplus::bar();
}
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You should never call virtual functions within a ctor, the result is undefined.
-Ben
---------
On the topic of code with no error handling -- It's not poor coding, it's "optimistic" 
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Is the alternative to say:
pMyThing = new Thing();
pMyThing->Init();
all the time? That would suck.
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Well, first off, polymophism is NOT the answer to every programming problem you might confront. So maybe for whatever it is you are trying to achieve you SHOULD be using C functions. I have no idea why you are defining your contstructors as inline, or what effect it has on the virtual calls. I've never seen that done before, and have no clue why you would need it. However, consider that the virtual table does not exist prior to the construction of the object. How would you expect a virtual call from the constructor to work? Obviously, as stated, it is undefined.
You do not need to call an "Init" function after the ctor, because the object should initialize itself IN the ctor. Each derived class, will probably have unique initialization demands which do not warrent a virtual call anyway.
If I really needed a "virtual constructor" (re: Stroustrup)which is essentially what you are trying to achieve here I would do something like this:
class foo {
foo(); //default constructor.
foo( foo& rfoo ); // copy constructor.
virtual foo* Clone(){ return( new foo( *this )); }
virtual bar();
};
class fooplus : public foo {
fooplus();
fooplus( fooplus& rfooplus );
virtual fooplus* Clone(){ return( new fooplus( *this )); }
virtual bar();
};
In this way, an object can always return a properly initialized copy of itself on demand.
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Thanks for your reply!
I don't think I've gone polymorphism happy (in the everything-looking-like-a-nail sense.)
My vision is to have code that says:
pObject = new MyFoobarizedZonkObject();
and I want the initialisation of the foobarized part of it to take place as a virtual function because there might also be a MyFoobarizedBlipObject whose foobarized part might be initialized a bit differently from MyFoobarizedZonkObject's. I guess you could take all the code that makes the objects foobarized and put it into its own class and use containment rather than inheritance, but this might or might not be natural. Does this make sense?
I don't know what I was thinking with the inline constructor except that I've just started using inline functions a lot and I'm used to putting 'inline' whenever I don't have the function defined in the cpp file. I know this isn't how it goes though and that 'inline' shouldn't be before the constructor declaration.
Saying 'virtual' before the 'bar' declaration in the fooplus class is also redundant, right?
I guess I don't quite see how the 'virtual constructor' would apply because I don't have a correctly initialized object to start with. What would the code look like to use it?
Thank you,
Alex
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The entire point of construction is to give an object the opportunity to uniquely initialize itself. Usually the way it is done is something like this:
class foo1
{
foo1() { m_x = 0; m_y = 0; m_y = 0; }
};
class foo2 : public foo1
{
// call the base class' constructor as you construct the derived class.
foo2(): foo1() { m_xx = 0; m_yy = 0; mm_zz = 0; }
};
class anotherfoo : public foo1
{
anotherfoo (): foo1() { m_xx = 0; m_yy = 0; mm_zz = 0; }
};
Now, both base and derived classs are properly initialize when you declare a foo2:
foouser::UseFoo()
{
foo2 footoo;
anotherfoo fooalso;
// or
foo2* pfootoo = new foo2();
anotherfoo* pfooalso = new anotherfoo();
};
So, I guess I don't really see what your issue is with initializing the objects. At this point, polymorphism has not even become
an issue.
The "Virtual Constructor" is simply a way to ensure a correct object is created if you do something like this:
(As I typically keep my objects in paramatarized lists, this technique comes in handy)
foouser::UseFoo()
{
foo2 footoo;
DoSomethingElse( &footoo );
}
foouser::DoSomethingElse( foo* pfoo )
{
foo* pfooX = pfoo->Clone();// pfoo creates a copy of a foo2, or anotherfoo, if it was called with that.
//// use pfooX.
//// Obviously, for this example, I could have just used pfoo as is, but say I wanted to store a foo2 in its
//// current state for whatever reason, this is very convenient. The point is that my Constructor is now capable of
//// polymorphic behavior.
delete pfooX;
};
I believe you are technically right about the derived virtual bar() being redundant. But the rule of thumb, I think, is once virutal, always virtual. You can keep yourself out of a lot of trouble by keeping that in mind.
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Yep, it sucks, but that's just the way it is.
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I've been caught out by this one in the past. What happens is that the object, although allocated enough space for a fooplus is first initialised as a foo object, then the foo constructor is called. At that point the foo virtual method table is in effect. Only once the foo constructor exits does the fooplus intialisation occur and the VMT switches to the one containing fooplus::bar. This behaviour is logical, fooplus::bar might refer to variables in fooplus that the foo constructor doesn't know to initialise.
How you get arround it depends on details of what you're doing that we don't know. If you're really getting into polymorphic programming you'll often find the best solution is static factory routines which give you a uniform access to constructors e.g.
<br />
<br />
class foo {<br />
protected:<br />
foo(...) {<br />
};<br />
public:<br />
static foo *factory( ... );<br />
virtual void bar();<br />
};<br />
<br />
class fooplus : public foo {<br />
protected:<br />
fooplus( ... ) : foo(plus) {<br />
}<br />
<br />
public:<br />
static foo *factory( ... );<br />
virtual void bar;<br />
..<br />
<br />
};<br />
<br />
foo *foo::facory( ... ) {<br />
foo *f = new foo( ...);<br />
f->bar();<br />
return f;<br />
}<br />
<br />
foo *fooplus::factory ( ...) {<br />
fooplus *f = new fooplus ( ...);<br />
f->bar;<br />
return f;<br />
}<br />
<br />
Because the factory methods are static and have the same signature you can store pointers to them in a table of variations on foo.
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How can I detect the state of a network card???????
I have try to use MIB_IFROW structure in PSDK, but don't know why, the only result I can get from this strcture is: unreachable.
WHy?
Any other solution?????
Send me a email if possible....
cheers
m0th@dcs.shef.ac.uk
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Is it possible for more than one window to be "active" in an MDI app? I ask because I need to have a toolbar send commands to all open views, not only the one active view. Possible? 
thanks,
Jake
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I don't think you want to do that by trying to make all open views active, even if you could. I assume you are using the Document/View architecture. If it were me, I would utilize your app's CDocument class, via the UpdateAllViews() call, to achieve that result, passing a hint to each view as to what toolbar command was sent. I have also seen people use the Main frame window to communicate commands to each open view - but I prefer CDocument. Just a suggestion.
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Thanks for the help - The UpdateAllViews is exactly what I want to do, except I can't get it to work for some reason. I'm basically doing something like:
The View catches the toolbar message, and a handler function is called. This function does some stuff and ends with: GetDocument()->UpdateAllViews(this, ENUM_VALUE1, NULL). Ideally this should call the OnUpdate() function of every open View, assuming I have an enum that allows ENUM_VALUE1.
However, OnUpdate never gets called. Passing "this" prevents it from being called on the active view, and nothing happens to the inactive views. I can't figure out why it's not doing anything 
thanks again,
Jake
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Unless all the views in your application share the same document, this approach will not work. You must first get a list of all the open documents, and then update all their respective views.
It might look something like the following;
CWinApp * pApp = AfxGetApp ();
ASSERT_VALID ( pApp );
POSITION posTemplate = pApp->GetFirstDocTemplatePosition ();
while ( NULL != posTemplate ) {
CDocTemplate * pTemplate = pApp->GetNextDocTemplate ( posTemplate );
ASSERT_VALID ( pTemplate );
ASSERT_KINDOF ( CDocTemplate, pTemplate );
POSITION posDocument = pTemplate->GetFirstDocPosition ();
while ( NULL != posDocument ) {
CDocument * pDocument = pTemplate->GetNextDoc ( posDocument );
ASSERT_VALID ( pDocument );
pDocument->UpdateAllViews ( NULL, ENUM_VALUE1, NULL );
}
}
-Ben
---------
On the topic of code with no error handling -- It's not poor coding, it's "optimistic" 
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Send the messages by way of the associated documents instead.
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I`m don`t think so, but some way to do this is to thru all your view using GetNetView, GetActiveview.
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Is there anyway in Win32 or MFC, to retrieve the current directory of the running application?
Anytime, I run GetCurrentDirectory, I get the default windows directory or my desktop directory depending on the platform.
thanks
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Use _getcwd ()
// GETCWD.C FROM MSDN
#include <direct.h>
#include <stdlib.h>
#include <stdio.h>
void main( void )
{
char buffer[_MAX_PATH];
if( _getcwd( buffer, _MAX_PATH ) == NULL )
perror( "_getcwd error" );
else
printf( "%s\n", buffer );
}
It is Illogical to define an inventor by his invention
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Why Word ignores the message WM_VSCROLL? Is there an alternative to this method for making Word scroll down its contents?
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hi all,
can you please tell me how to include the source code given int his site can be used in my application;)
i would like to experiment
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I'm not sure what you're asking. Copy the class you want to use into your project directory, add it to the project (projectg/add/files from memory), and use it.
Jonathon
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I am having problems using the DirectSound API. The problem is that sometimes my program attaches itself to the soundbuffer and does not release it. This prevents any other device from accesing the buffer.
Does anyone know what I am doing wrong??
Also, is there an easier way to stream audio?? I have DIS packets containing sound data that I need to stream. Is there a way to use the ActiveX Windows multimedia component to stream audio data that is not coming fram a file??
Please help me if you have any ideas....
Daniel Selberg
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Netmeisters,
I am having a great deal of difficulty doing something with VC++ which
should be very simple, and would appreciate your help. All I would
like to do is, create a static library and link an application to it
(as I said, it should be very simple...). The static library contains
C type functions, rather than C++ classes.
I create the library, we'll call it foo, by selecting New Project |
Win32 static library, and leaving the two options (MFC support and
precompiled headers) unchecked. Then I create two files, foo.h and
foo.c, in the library. The first just contains
void bar(void);
and the second
void bar() { }
This compiles OK, creating the file foo.lib. Now if I want to use
bar() in an application, I should just have to include foo.h and
specify a link to foo.lib. I do the latter by using Project | Add to
Project | Files, after which foo.lib shows up in the pane on the left
under Resources. When I compile the application, however, the include
file gets read (because there are no complaints about bar being
undefined), but the linker complains that bar is an unresolved symbol.
I have example code from a book showing how to do this, and the code
compiles just fine. Also, if I add my function bar() to the example
code, everything works as expected. If I declare bar() in my include
file, but define it in the example library, everything works fine. But
for some reason I can't define it in my own library; linking just
doesn't work.
There must be some straightforward way of making all this work, but
for the life of me I can't figure it out. This kind of thing is real
simple under Unix, don't know what is going wrong under Windows. Would
very much appreciate some assistance.
Thanks,
Matthew Fleming
------------------------------------------------------------------------------
Matthew G. Fleming, MD phone : 414.456.4072
Associate Professor fax : 414.456.6518
Department of Dermatology s-mail: Dept. of Dermatology
Medical College of Wisconsin Medical College of Wisconsin
MFRC Room 4061
e-mail: mgf@mcw.edu Milwaukee, WI 53226-4810
------------------------------------------------------------------------------
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Generally speaking, the issue has to do with the "name mangling" a c++ compiler imposes. I beleive if you use:
extern "C" {
Func1();
Func2();
etc }
or
extern "C"
{
#include <my_c_header.h>
}
you should get better results.
MSDN has some info on this if you want more. I have not dealt with this since way back in my 16 bits days, but I think that is what you are probably running into.
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I think you need to add your library in Project|Settings...|Link in category Input in the Object/Library modules field.
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I want to use MS Agent control in my Dialog Base App.... and I don't know... your help is big.. please put it to my project...
Contact me by mail if you want to develop with me!!!!
nikado@pc.nu
/*
BETA
*/
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