C / C++ / MFC

18-Apr-24 8:34

UPDATE / closed - no solution found.

This was pretty futile task, there are few "private" objects I did not see until
each "parent" level was expanded.

This is an offshoot of my other post
AND
if it is NOT OK for me to continue posting - there are others who are commenting negatively
about my too many posts"

PLEASE

DO NOT REPLY

I do not want to waste "volunteers time ".

I am currently working on nested objects

main object ( patent _)
secondary object ( child )
next object ( child )

I am trying to pass correct parameters between them
I am debugging the flow using constructors and
it looks as the compiler / linker access / flow in sort of backwards

First trace is "next object " constructor ....
and then I get lost tracing....UP next object

is that normal ?

That is all I wanted to ask.

Thanks

modified 2 days ago.

Mircea Neacsu18-Apr-24 9:13

18-Apr-24 9:13

I assume your question is about the order of initialization of compound objects.

C++

#include <iostream>
using std::cout;

class level3 {
public:
  level3(const std::string& name);
};

class level2 {
public:
  level2(const std::string& name);

private:
  level3 grandchild;
  level3 favourite_grandchild;
};

class top_level {
public:
  top_level(const std::string& name);

private:
  level2 child;
  level2 other_child;
};

top_level::top_level(const std::string& name)
  : other_child("other_child") //this will be called AFTER initialization of 'child'
  , child("child")         //this is called first because 'child' is declared first
{
  cout << name << " constructor\n";
}

level2::level2(const std::string& name)
  : favourite_grandchild("favourite_grandchild") //this is again called AFTER the next line
  , grandchild("grandchild")                     //this is called first
{
  cout << name << " level2 constructor\n";
}

level3::level3(const std::string& name)
{
  cout << name << " level3 constructor\n";
}

int main()
{
  top_level t("top");
}

The result is this:

grandchild level3 constructor
favourite_grandchild level3 constructor
child level2 constructor
grandchild level3 constructor
favourite_grandchild level3 constructor
other_child level2 constructor
top constructor

In words: aggregate objects initialize their members in the order in which the members are declared, not in the order of initializers in the constructor of the aggregate. After initializing all members, the constructor code is run.

Mircea

Salvatore Terress18-Apr-24 14:57

18-Apr-24 14:57

Many thanks for helping me to analyze the problem.

I now have a better understanding what is going on and have found a part of the problem.

Here my current partial trace

19:45:53: Debugging /mnt/A_BT_DEC10/A_APR13_APR15/A_APR9_MAR7_MAR19_CLEAN/A_BT_LIBRARY/mdi/mdi ...
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
" #ifdef CONNECT  START constructor A_BT_TAB_DIALOG::A_BT_TAB_DIALOG(QWidget *)"
" #ifdef CONNECT  END constructor A_BT_TAB_DIALOG::A_BT_TAB_DIALOG(QWidget *)"
"          #ifdef CONNECT  ZTART CONSTRUCTOR SettingsDialog::SettingsDialog(QWidget *) @ line # 88"
"       #ifdef CONNECT  END CONSTRUCTOR SettingsDialog::SettingsDialog(QWidget *) @ line # 229"
" #ifdef CONNECT  START constructor A_BT_TAB_DIALOG::A_BT_TAB_DIALOG(QWidget *)"
" #ifdef CONNECT  END constructor A_BT_TAB_DIALOG::A_BT_TAB_DIALOG(QWidget *)"
"          #ifdef CONNECT  ZTART CONSTRUCTOR SettingsDialog::SettingsDialog(QWidget *) @ line # 88"
"       #ifdef CONNECT  END CONSTRUCTOR SettingsDialog::SettingsDialog(QWidget *) @ line # 229"

and it shows that both objects are "constructed " twice...

Salvatore Terress19-Apr-24 4:00

19-Apr-24 4:00

ADDENDUM

I am still trying to learn how to pass parameters to object.

My current "duplicating constructor" is because I am doing
it wrong.

My main object constructor is defined this way:

C++

MainWindow_Bluetooth::MainWindow_Bluetooth(QWidget *parent) :
       QMainWindow(parent),
       m_ui(new Ui::MainWindow_Bluetooth),
       m_status(new QLabel),
       m_console(new Console),
       // insert MDI area here ??
       m_mdiarea(new QMdiArea),

       m_settings(new SettingsDialog),
       //! [1]
       //! add rfcomm ??
       m_serial(new QSerialPort(this))
      // sequence 1st add HERE
      // must bbe passed to SettingsDialog
       // this is wrong parameter here ??
       //m_TAB_Connect(new A_BT_TAB_DIALOG),
       //m_TAB_Ext(new A_BT_TAB_DIALOG_EXT)


     //! [1]
   { // function apply \

hence I am passing settings(new SettingsDialog),
as a parameter.

SettingsDialog constructor:

C++

SettingsDialog::SettingsDialog(QWidget *parent) :
    QDialog(parent),
    m_ui(new Ui::SettingsDialog),
    m_status(new QLabel),
    // 3 sequence  add dialogs
    // HERE wrong  object
    m_TAB_Connect(new A_BT_TAB_DIALOG),
    // wrong  object
    m_TAB_Ext(new A_BT_TAB_DIALOG_EXT),
    m_intValidator(new QIntValidator(0, 4000000, this))
{

its in question / problem passed parameter is

m_TAB_Connect(new A_BT_TAB_DIALOG),

now for the source of this problem

I have TWO instances of SettingsDialog
and they point to TWO instances of A_BT_TAB_DIALOG
hence I end up with WRONG instances of A_BT_TAB_DIALOG

Can I modify my code to have TWO instances of A_BT_TAB_DIALOG
and make sure I point to the CORRECT instance ?

In my not so technical terminology
can I pass a parameter to
have something like

m_TAB_Connect(new A_BT_TAB_DIALOG),

m_TAB_Connect_Ext(new A_BT_TAB_DIALOG),

I am looking for a solution and I am open tor suggestions
leading to proper C++ solution.

Thanks

Mircea Neacsu19-Apr-24 4:31

19-Apr-24 4:31

Salvatore Terress wrote:
Can I modify my code to have TWO instances of A_BT_TAB_DIALOG
and make sure I point to the CORRECT instance ?

What do you mean by "correct"?

In your code:

C++

SettingsDialog::SettingsDialog(QWidget *parent) :
    //
    // ... stuff
    //
    m_TAB_Connect(new A_BT_TAB_DIALOG), // creates a A_BT_TAB_DIALOG
    m_TAB_Ext(new A_BT_TAB_DIALOG_EXT), // creates a A_BT_TAB_DIALOG_EXT
    // ...
{

If you have somewhere:

C++

SettingsDialog obj1(parent);
SettingsDialog obj2(parent);

each one of them will have their own TAB_Connect and TAB_Ext. In other words obj1.m_TAB_Connect != obj2.m_TAB_Connect.

Do you want both of them to point to the same TAB object?

Mircea

Salvatore Terress19-Apr-24 7:11

19-Apr-24 7:11

I am sorry - I should have deleted the _Ext .
Currently I am asking about the

variable( new object )

syntax

elsewhere.

I have a hard time finding /searching for it

I just need a verbal expiation of THIS specific form / syntax
or real reference to it.

Mircea Neacsu19-Apr-24 7:43

19-Apr-24 7:43

If you have an object like this:

C++

class Thing1 {
public:
  Thing1 ();
}

You can use it in another object:

C++

class Composite {
public:
  Composite ();
private:
  Thing1* part;
};

Composite::Composite()
  : part (new Thing1)
{
}

In Composite, the member part is a pointer to a Thing1. When a composite is constructed, first the program allocates on heap a new object of type Thing1 and invokes it constructor. Because constructor for Thing1 does not have any parameters there is no need for a list of parameters.

Next step:
You have another type of object Thing2 declared like:

C++

class Thing2 {
public:
  Thing2 (int param=42);
};

and the Composite object has 2 members:

C++

class Composite {
public:
  Composite ();
private:
  Thing1* part;
  Thing2* other_part;
};

The constructor of Composite could be:

C++

Composite::Composite ()
  : part (new Thing1) //as before
  , other_part (new Thing2) //same as saying other_part(new Thing2(42))
{}

because now the constructor for Thing1 needs a parameter but the parameter has a default value and the compiler will call the constructor with said value. Obviously, if you need a different value for the parameter, you will have to add it:

C++

Composite::Composite ()
  : part (new Thing1) //as before
  , other_part (new Thing2(24) //explicit constructor parameter
{}

Going back to the original question (which you seem to have deleted)
What you want to have is it something like:

C++

class Composite{
public:
  Composite ();
private:
  Thing1 *part;
  Thing1 *other_part;
{}

? Try to rephrase your question it terms of simple objects to make it easier for us to understand.

Mircea

k505419-Apr-24 8:16

k5054

19-Apr-24 8:16

Lets break this down:
1) The expression new Object creates a new instance of Object on the heap, and provides a pointer to the new object.
2) The expression foo( something ) makes a function call. We might be able to deduce that m_status() is a member function to some object, both from your descriptions elsewhere and the use of the m_ decoration, but that's not necessarily the case. It could be you are using m_ as a decoration for a menu object or a motorhome object or some other mystery object....

Together we have f(new Object) which (1) constructs a new Object on the heap, and then (2) calls a function f with a pointer to the newly constructed Object. What we don't know is if Object has a default constructor. It might not, in which case, as you observe over in the lounge, you must use f(new Object(param, ...). There may be multiple constructors, so you'll need to check the documentation for the Object to see which one is most appropriate.

If you create an object with new, at some point delete Object should to be used to recover the allocated memory¹. It's seems unlikely the the called function would do that, as it cannot know whether the pointer to Object is a pointer to a stack or heap object. Trying to delete a stack object is almost certainly going to cause Bad Things™ to happen. Maybe an immediate abort, maybe an exception gets thrown or maybe just a silent mess up of your data, with no indication that bad things have happened until some time later in the program. So you're probably better off to not use new Object as a parameter to a function. In general you should prefer a smart pointer ( Dynamic memory management - cppreference.com ) to new/delete in new development. But maybe the function does expect its parameter to be newly constructed within the parameter list and will delete before it returns? We don't know.

Footnotes:
¹ This isn't strictly true. If you only create one instance of an object, the memory will be recovered when the program exits. A number of GNU C stdlib routines do this, allocating a block of memory when first called and re-using it as needed. The allocated memory is only "lost" to the executing program - assuming virtual memory and one of the usual operating systems (e.g. window, linux, macos, etc). That might not be true for some specialized use operating systems or for "stand-alone" programming environments.

"A little song, a little dance, a little seltzer down your pants"
Chuckles the clown

Salvatore Terress19-Apr-24 9:48

19-Apr-24 9:48

Thank you, that is exactly what I was asking about.
Plain explanation,,,,
I need to digest the "pointer to the object ".

My program just broke big time , so I am busy trying find where...
I have backup , but not up - to date...
Thanks again...

PS
I need to stay away from lounge, those folks are in their own world ,,,
definitely not same as mine

k505419-Apr-24 10:58

k5054

19-Apr-24 10:58

Salvatore Terress wrote:
I need to digest the "pointer to the object ".

That's worrisome. That's basic C/C++ stuff. Something any programmer with more than a few weeks experience should at least have some familiarity with. You should also understand the relationship between a pointer and a reference.

Salvatore Terress wrote:
My program just broke big time , so I am busy trying find where...
I have backup , but not up - to date..

Get yourself hooked up with a version control system like Git or SVN. There are public servers for both. If you need to keep you code proprietary (or just don't wish to share), either can be set up locally. If you need a local SVN/Git server, that might be a great project for a PI. If you're using QDevelop, then a quick google suggests that it supports several Version Control systems. Even if you're the only developer, being able to review and/or revert can save you a whole bunch of time. And red faces.

"A little song, a little dance, a little seltzer down your pants"
Chuckles the clown

Salvatore Terress20-Apr-24 15:38

20-Apr-24 15:38

Sorry, bu I need more explanations /help .

Here is my class constructor

C++

SettingsDialog::SettingsDialog(QWidget *parent) :
    QDialog(parent),
    m_ui(new Ui::SettingsDialog),
    m_status(new QLabel),
 
    m_TAB_Connect(new A_BT_TAB_DIALOG),
    
    //m_TAB_Ext(new A_BT_TAB_DIALOG_EXT),
    m_intValidator(new QIntValidator(0, 4000000, this))
{

here is a snippet of class definition

A_BT_TAB_DIALOG *m_TAB_Connect = nullptr;

you said that
new A_BT_TAB_DIALOG),

builds a pointer - to object A_BT_TAB_DIALOG

and

m_TAB_Connect(new A_BT_TAB_DIALOG),

is a function call of function

m_TAB_Connect

that is not what I thought is happening
and I hope it is not some kind of Qt "stuff"

I am reading

m_TAB_Connect(new A_BT_TAB_DIALOG),

as

passing pointer m_TAB_Connect of (new) object A_BT_TAB_DIALOG

am I wrong?

I am not trying to nitpick, but I am having an issue accessing correct instance of
the parent class AND NEED to get this terminology correct.

Richard MacCutchan21-Apr-24 2:04

Richard MacCutchan

21-Apr-24 2:04

Let's try and look at this set of parameters line by line
1. Why are you calling QDialog here? That line of code creates a new QDialog object, but you do not save any pointer to it, so what is the reason for that?

C++

QDialog(parent),

2. I assume that m_ui is declared as a pointer to a Ui::SettingsDialog which you will refer to somewhere later.

C++

m_ui(new Ui::SettingsDialog),

3. As with point 2 you create a new object whose pointer you store in m_status.

C++

m_status(new QLabel),

4. Possibly the same as 2 and 3 but I have no idea what m_TAB_Connect is. Is it a pointer, or a method?

C++

m_TAB_Connect(new A_BT_TAB_DIALOG),

5. Same as comment 4.

C++

m_intValidator(new QIntValidator(0, 4000000, this))

So without further details of the class it is impossible to say whether this is correct or not. Constructors really should do the minimal initialisation necessary to create the object, that is just setting properties that do not require callouts to other classes. Any calls to other constructors, methods, API functions etc. is generally best left to an initialisation method.

Maximilien19-Apr-24 4:13

Maximilien

19-Apr-24 4:13

If I understand your question correctly.

Constructors will (try to) construct derived objects before itself

ie. the base object needs to be constructed to be able to construct the derived classes.

class Base {};
class Child : public Base{}

Base will be constructed before Child.

CI/CD = Continuous Impediment/Continuous Despair

Salvatore Terress19-Apr-24 14:01

19-Apr-24 14:01

Correct - that is why I used term "nested objects ".
My goal is to have an application with logical , intuitive GUI . hence I have sort of main parent GUI object with children.
I am using " cut and paste " example which is "pop=up" dialog based , and I have added another windowing part to it.
Unfortunately I did not keep better track of these , basically TWO parallel methods.
And that what caused the problem.
With so much help received I am sure I can adjust my code to avoid further disasters..
and I do appreciate the help, very much.

Can a locale be Removed from a basic_ostream Subsequent to basic_ostream.imbue(locale)

Richard MacCutchan19-Apr-24 6:32

Richard MacCutchan

19-Apr-24 6:32

This is a reply to your question in the Lounge, which as you well know is not the place for programming questions.

Salvatore Terress wrote:
where to find decent description of the
this syntax
m_status(new QLabel),

It is part of the constructor for a MainWindow_Bluetooth object. And since that line follows the set of initializers, it means create a new QLabel object, and store its pointer in the variable m_status. Why you are doing that, only you can answer.

Bottom line, study the documentation for C++ classes, where all the syntax is explained.

BernardIE531717-Apr-24 1:48

BernardIE5317

17-Apr-24 1:48

Greetings Kind Regards

Please consider the C++ code below. It is utilized it to generate a locale formatted number e.g. "1,234". However subsequent I wish again to generate a number but not so formatted e.g. "1234". So I inquire can an imbued locale be removed from an output stream so no such locale specific formatting occurs. Of course another stream which has not been so imbued can be utilized for this purpose but prefer not to do so as such seems a less elegant solution.

Thank You Kindly

basic_ostringstream<char> _ostream;
_ostream.imbue(locale("en-US"));
_ostream << 1234;

Re: Can a locale be Removed from a basic_ostream Subsequent to basic_ostream.imbue(locale)

Mircea Neacsu17-Apr-24 2:03

Re: Can a locale be Removed from a basic_ostream Subsequent to basic_ostream.imbue(locale)

17-Apr-24 2:03

C++

_ostream.imbue(std::locale::classic());

If you want to be standard abiding, names prefixed with "_" are reserved in global namespace.

I can hear "man, is this guy pedantic!" Laugh | :laugh:

Mircea

BernardIE531717-Apr-24 11:55

BernardIE5317

17-Apr-24 11:55

May I please inquire how you would name the variable. It is my custom to utilize prefix '_' for identifiers of objects of standard template library types for brief simple functions as the purpose of such object is obvious in such situations instead of a lengthy explanatory name which I reserve for more lengthy more complicated functions.

Re: Can a locale be Removed from a basic_ostream Subsequent to basic_ostream.imbue(locale)

Mircea Neacsu17-Apr-24 12:14

17-Apr-24 12:14

It's a question of taste: put the underscore at the other end (ostream_), or come up with a different name (ostrm). As in any question of taste, there isn't any right answer; my personal preference goes for trailing underscore.

The rule about leading underscore is not my invention. See C++ Language standard section 17.6.4.3.2 - Global names (page 429).

Mircea

how to add new class ?

Salvatore Terress16-Apr-24 13:32

16-Apr-24 13:32

I am seriously trying to learn more about C++_.

I did add a new class to the constructor, just following an examples , and
I do not understand why I am getting this error.

My own add is duplicate of existing , working class,

and I do no see why
it does no like the pointer.

m_serial(new QSerialPort(this),
  // sequence 1` st add HERE
   m_TAB_Ext(new A_BT_TAB_DIALOG_EXT)

/mnt/A_BT_DEC10/A_APR13_APR15/A_APR9_MAR7_MAR19_CLEAN/A_BT_LIBRARY/terminal_Bluetooth/mainwindow_Bluetooth_copy.cpp:3088: error: called object type 'A_BT_TAB_DIALOG_EXT *' is not a function or function pointer
mainwindow_Bluetooth_copy.cpp:3088:22: error: called object type 'A_BT_TAB_DIALOG_EXT *' is not a function or function pointer
            m_TAB_Ext(new A_BT_TAB_DIALOG_EXT())
            ~~~~~~~~~^

here is my class declaration

C++

namespace Ui {
class A_BT_TAB_DIALOG_EXT;
// add forward declarations ??
class  QMdiArea;
}

class A_BT_TAB_DIALOG_EXT : public QWidget
{
    Q_OBJECT

public:
    explicit A_BT_TAB_DIALOG_EXT(QWidget *parent = nullptr);
    ~A_BT_TAB_DIALOG_EXT();

private:
    Ui::A_BT_TAB_DIALOG_EXT *ui;

    // 3 define / declare members / parameters

    QLabel *m_status = nullptr;
    QMdiArea *m_mdiarea = nullptr;
    QSerialPort *m_serial = nullptr;


};

Mircea Neacsu16-Apr-24 13:44

16-Apr-24 13:44

There is a slight discrepancy in your code. You wrote:

C++

m_serial(new QSerialPort(this),
  // sequence 1` st add HERE
   m_TAB_Ext(new A_BT_TAB_DIALOG_EXT)

Meanwhile the compiler error message is:

m_TAB_Ext(new A_BT_TAB_DIALOG_EXT())

(note the extra pair of parenthesis).

The code you posted is potentially correct, assuming m_TAB_Ext is declared as:

C++

A_BT_TAB_DIALOG_EXT *m_TAB_Ext;

However the compiler error message seems to indicate that you have those extra parenthesis and, in this case, the compiler interprets it as a function call.

Mircea

Salvatore Terress16-Apr-24 15:11

16-Apr-24 15:11

Good catch, but even after removing the () I get same error.

//! [1]
      //! add rfcomm ??
      m_serial(new QSerialPort(this),
     // sequence 1` st add HERE
      m_TAB_Ext(new A_BT_TAB_DIALOG_EXT)

Mircea Neacsu16-Apr-24 15:23

16-Apr-24 15:23

Not sure I understand what you try to do. Maybe the code samle is a bit too short. Where is the `m_TAB_ext` initialization line? I don;t see a declaration for `m_TAB_ext`.

Mircea