C / C++ / MFC

15-Jan-24 7:41

Minor add:

I think the loop increment is wrong

I have commented out inner loop and addend two more list to the array
so the decimal count should be 5.
OK the code say Array size 4
and it misses the last array.
That should be a snap to fix...

<"TASK #ifdef FUNCTION_TEST_PROJECT int MainWindow_Bluetooth::CreateMenus_Array()79"
" index array 0  Array size 4"
" index array 1  Array size 4"
" index array 2  Array size 4"
" index array 3  Array size 4"/pre>








OK, I have plain C question about nested  "loop" 

My task is to loop thru two dimensional array...
The error in my code is stopping the embedded loop.

Here is a snippet of the run debug messages

here is the "problem " code 

 for (index_main = 0; index_main < list_array[index_array][index_main].size(); ++index_main)
What am I doing wrong in sizing the array?
Many thanks for help resolving this.

Debug


 <pre lang="text">" index array 0Array size 4"
" main menus  0 SubWindow terminal     (QMdiArea )main menu size 34"
" main menus  1 SubWindow hcitool      (QMdiArea )main menu size 34"
" main menus  2 SubWindow bluetoothctl (QMdiArea )main menu size 34"
" main menus  3 SubWindow system       (QMdiArea )main menu size 34"
ASSERT failure in QList<T>::operator[]: "index out of range", file /home/nov25-1/Qt/5.15.2/gcc_64/include/QtCore/qlist.h, line 575
12:23:02: /mnt/A_BT_DEC10/BT__PROGRAMS/A_JAN11/A_BT_LIBRARY/mdi/mdi crashed.

Array;

C++

const QStringList list_array[10]
   {
       { "SubWindow terminal     (QMdiArea )",
           "SubWindow hcitool      (QMdiArea )",
           "SubWindow bluetoothctl (QMdiArea )",
           "SubWindow system       (QMdiArea )" },

       { "SubsubWindow bluetoothctl help        (QMdiArea )",
           "SubsubWindow bluetoothctl list  (QMdiArea )",
           "SubsubWindow bluetoothctl devices (QMdiArea )",
           "SubsubWindow bluetoothctl show  (QMdiArea )" },

       { "SubsubWindow hcitool        (QMdiArea )",
           "SubsubWindow hcitool   dev  (QMdiArea )",
           "SubsubWindow hcitool   scan (QMdiArea )",
           "SubsubWindow hcitool   inq  (QMdiArea )"}
   };

Code:

C++

for (index_array = 0; index_array <  list_array[index_array].size(); ++index_array  )
 {
     text = " index array ";
     text += QString::number(index_array);
     text += "Array size ";
     text += QString::number(list_array[index_array].size() );
     qDebug() << text;

 for (index_main = 0; index_main < list_array[index_array][index_main].size(); ++index_main)
 {
     text = " main menus  ";
     text += QString::number(index_main);
     text += " ";
     text += list_array[index_array][index_main];
     text += "main menu size ";
     text += QString::number(list_array[index_array][index_main].size());
     qDebug() << text;
 }
 }

modified 15-Jan-24 18:16pm.

jeron115-Jan-24 9:31

jeron1

15-Jan-24 9:31

I've never used Qt before but, this line seems odd,

for (index_array = 0; index_array <  list_array[index_array].size(); ++index_array  )

specifically

index_array <  list_array[index_array].size()

Maybe try something like

for (index_array = 0; index_array <  list_array.size(); ++index_array  )

"the debugger doesn't tell me anything because this code compiles just fine" - random QA comment
"Facebook is where you tell lies to your friends. Twitter is where you tell the truth to strangers." - chriselst
"I don't drink any more... then again, I don't drink any less." - Mike Mullikins uncle

modified 15-Jan-24 15:38pm.

Salvatore Terress15-Jan-24 9:50

15-Jan-24 9:50

Sorry, no go.

This is not about Qt - I no longer post questions about Qt - this is wrong forum for Qt.

This is plain C question - hence in "C..." sub forum.

In my view each loop has its stopping point.

The first - parent loop - needs to stop when it reaches the end

AND its "size" is correct (see debug message ) and I can run it bypassing the "inner " loop.

The size of inner loop is wrong - see debug messages posted.

Changing the parent loop size as suggested gets this error:

/mnt/A_BT_DEC10/BT__PROGRAMS/A_JAN11/A_BT_LIBRARY/terminal_Bluetooth/mainwindow_Bluetooth.cpp:142: error: member reference base type 'const QStringList[10]' is not a structure or union
mainwindow_Bluetooth.cpp:142:52: error: member reference base type 'const QStringList[10]' is not a structure or union
    for (index_array = 0; index_array <  list_array.size(); ++index_array  )
                                         ~~~~~~~~~~^~~~~

k505415-Jan-24 10:45

k5054

15-Jan-24 10:45

I think you've got your logic in a twist here. I think it should be

C++

for(index_array = 0; index_array < list_array.size(); ++index_array )
{
    // stuff
    for(index_main = 0; index_main < list_array[index_array].size(); ++index_main ) 
    {
       // more stuff
    }
}

Additionally, note that you're calculating list_array.size() and list_array[index_array].size() multiple times. Perhaps better would be

C++

const size_t list_max = list_array.size();
for( index_array = 0; index_array < list_max; ++index_array )
{
   // stuff
   const size_t array_max = list_array[index_array].size();
   for(index_main = 0; index_main < array_max; ++index_main)
   {
      //more stuff 
   }

Maybe, since you've declared list_array as const, the compiler will be able to optimize away the unneeded function calls, but speaking for myself, I find my version just a little easier to read and understand.

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

Salvatore Terress15-Jan-24 12:28

SOLVED Re: Loop thru two dimensional array - edited

15-Jan-24 12:28

Sorry, but the compiler till complain about this - without specifying it is an arraray as [10]

/mnt/A_BT_DEC10/BT__PROGRAMS/A_JAN11/A_BT_LIBRARY/terminal_Bluetooth/mainwindow_Bluetooth.cpp:168: error: member reference base type 'const QStringList[10]' is not a structure or union
mainwindow_Bluetooth.cpp:168:39: error: member reference base type 'const QStringList[10]' is not a structure or union
    const size_t list_max = list_array.size();
                            ~~~~~~~~~~^~~~~

const size_t list_max = list_array.size();
 for( index_array = 0; index_array < list_max; ++index_array )
 {
    // stuff
    const size_t array_max = list_array[index_array].size();
    for(index_main = 0; index_main < array_max; ++index_main)
    {
       //more stuff
    }
 }

Salvatore Terress15-Jan-24 12:49

Re: SOLVED Re: Loop thru two dimensional array - edited

15-Jan-24 12:49

SOLVED
Wrong logic in embedded loop - this is size of CURRENT / dynamic MAIN loop member.

Thanks very much for all the help.
Sal

C++

for (index_array = 0; index_array <  list_array[index_array].size()+1; ++index_array  )
{
    text = " index array ";
    text += QString::number(index_array);
    text += "  Array size ";
    text += QString::number(list_array[index_array].size() );
    qDebug() << text;

for (index_main = 0; index_main < list_array[index_array].size(); ++index_main)
{
    text = " main menus  ";
    text += QString::number(index_main);
    text += " ";
    text += list_array[index_array][index_main];
    text += "main menu size ";
    text += QString::number(list_array[index_array][index_main].size());
    qDebug() << text;
}
}

return 0;

{// menus processing

Found the cause of the weird count

The code counts # of characters in the member of the child array....

" index array 0 Array size 7"
" main menus 0 SubWindow terminal added space here (QMdiArea )main menu size 57"
" main menus 1 SubWindow hcitool (QMdiArea )main menu size 34"
" main menus 2 SubWindow bluetoothctl (QMdiArea )main menu size 34"
" main menus 3 SubWindow terminal (QMdiArea )main menu size 34"
" main menus 4 SubWindow hcitool (QMdiArea )main menu size 34"
" main menus 5 SubWindow bluetoothctl (QMdiArea )main menu size 34"
" main menus 6 SubWindow system (QMdiArea )main menu size 34"
ASSERT failure in QList<t>::operator[]: "index out of range", file /home/nov25-1/Qt/5.15.2/gcc_64/include/QtCore/qlist.h, line 575

modified 15-Jan-24 19:10pm.

jeron116-Jan-24 6:39

jeron1

16-Jan-24 6:39

To me anyway, your for loop test seems tailored to the actual counts of items and subitems, what if each QStringList had 15 strings instead of 4?

Couldn't you use containers analogous to stl contianers
something along the lines of;

QList<QStringList> myList;

QStringList strlist1 = { "Blah1", "Blah2", "Blah3" };
QStringList strlist2 = { "Blah4", "Blah5", "Blah6" };
QStringList strlist3 = { "Blah7", "Blah8", "Blah9" };

myList.push_back(strList1);
myList.push_back(strList2);
myList.push_back(strList3);

  for (int mainIndex = 0; mainIndex < myList.size(); mainIndex++)
  {
     // do item stuff
  
     for (int subIndex = 0; subIndex < myList[mainIndex].size(); subIndex++)
     {
        // do some sub item stuff
     }
  }

Re: SOLVED Re: Loop thru two dimensional array - edited

Salvatore Terress16-Jan-24 7:20

Adding "checkable " in Qt QMenu / QAction using C++ partially fails

16-Jan-24 7:20

Yes, pretty much similar code.
..and the idea of "variable count ", I will eventually have a file where I will keep the data and will add to it as required - sort of database .
I messed up a little and had the main loop in the array...
It has been great "discussion" and it helped a lot...
Thanks

PS
I may post the final version ,if anybody cares.
Right now it is lot of "cut and paste" to put it in code
which actuality does puts menu /submenu into main code.

Salvatore Terress13-Jan-24 16:29

Re: Adding "checkable " in Qt QMenu / QAction using C++ partially fails

13-Jan-24 16:29

SOLVED
EDIT
voluntarily removed irrelevant code.

modified 15-Jan-24 13:11pm.

Richard MacCutchan13-Jan-24 21:09

Richard MacCutchan

13-Jan-24 21:09

Sorry, but this has nothing to do with C++. Whether you like it or not this is a Qt issue, and the Qt forums are the best place for the question.

Re: Adding "checkable " in Qt QMenu / QAction using C++ partially fails

Dave Kreskowiak14-Jan-24 6:06

Dave Kreskowiak

14-Jan-24 6:06

Quote:
I am using QtCreator and if you are NOT familiar with Qt - please do not tell me to post it in Qt forum.
I have DONE that a getting nowhere fast... I am getting the usual "you do not know what you are doing"
or RTFM.

The problem with your statement is that you are assuming everyone who uses C++ is also using Qt, which is simply not the case. By not using the Qt forums, you are severely restricting the number of Qt users who can see your question, and you're waiting on the fewer people with Qt experience around here to stumble on your question. Not everyone here visits the site every single day.

Asking questions is a skill
CodeProject Forum Guidelines
Google: C# How to debug code
Seriously, go read these articles.
Dave Kreskowiak

Re: Adding "checkable " in Qt QMenu / QAction using C++ partially fails

jschell15-Jan-24 4:00

jschell

15-Jan-24 4:00

Googling with the following gives results that look like they have examples of menu creation.

"QAction" example sub menu

Other than that given multiple questions that you have about it. You might consider the following
1. Use something else
2. The source code is available. So you can dive into that to find solutions to your problems.

I will note that I do in fact use 2 quite often. Both for Java VM (and libraries) and C# Microsoft libraries. So it is not a flippant answer. Documentation is almost never sufficient for all cases. Looking at the source code provides solutions. (Or at least in a couple of cases proved that my current solution would not work.)

Re: Adding "checkable " in Qt QMenu / QAction using C++ partially fails

Salvatore Terress15-Jan-24 7:06

memory allocation failure

15-Jan-24 7:06

The issue was /is the relations between QMenu and QAction...I did solved this by looking at many similar examples. But as told many times - posting it here was my mistake, lesson learn.
Thanks.

mike741111-Jan-24 1:28

mike7411

11-Jan-24 1:28

If a memory allocation with new fails in C++, should it return NULL or throw an exception?

I have this code:

C++

#include <iostream>
#include <vector>
#include <unistd.h>
using namespace std;

int main() {
    try{
    char *p = new char[44'321'833'923];
    
     if (!p) {
        cout << "memory allocation failed";
        exit(1);
        
    }
    
    }
    catch(exception&e)
    {
        cout << "caught it." << e.what();
        exit(1);
    }
    catch (...)
    {
        cout << "caught exception;";
        exit(1);
    }
    
 
	return 0;
}

The class I'm taking says it returns NULL, but the code seems to throw an exception.

Anyone know?

Thanks.

Mircea Neacsu11-Jan-24 1:37

Mircea Neacsu

11-Jan-24 1:37

I don’t know who teaches the class you are taking but I hope you don’t pay much for it. new has been throwing std::bad_alloc for the past 20+ years.

Also, while I don’t mind at all answering your questions, why don’t you try to googling? A search for “c++ new allocation failure” gives you many results and undoubtedly can teach you more than my limited answers.

Edit: Using exactly the search I suggested, I found this good article that discusses the issue: C++ Exceptions and Memory Allocation Failure[^].

Mircea

modified 11-Jan-24 7:50am.

mike741111-Jan-24 3:28

mike7411

11-Jan-24 3:28

The class is right here:

https://www.edx.org/learn/computer-programming/iitbombay-programming-basics

Here is some code from the class:

C++

int main()
{
int numStudents;
int * A;
cin >> numStudents;
A = new int[numStudents];
if (A != NULL) { A[0] = 10; A[1] = 15;}
return 0;
}

Richard MacCutchan11-Jan-24 3:35

Richard MacCutchan

11-Jan-24 3:35

As this is supposed to be a C++ class, the code should be using nullptr rather than the old Windows NULL definition. And what happens if numStudents is only 1?

Mircea Neacsu11-Jan-24 3:40

Mircea Neacsu

11-Jan-24 3:40

Colour me not impressed! As long as you take the free option, I guess you didn't loose much, except maybe some time. Also there is the question of getting bad programming habits, but those can be fixed over time.

These days there are many free online course from very reputable sources like MIT OpenCourseWare | Free Online Course Materials[^]. You might want to take a look at some of them.

Mircea