C / C++ / MFC

called pointer is null...

29-Oct-23 4:48

After some "RTFM" I came up with this code

C++

if(inString.contains("Agent") & inString.contains("registered") )
       {
           text = "Match ";
       }else
       {
           text = " No match ";
       }


       qDebug() << text;
       textDEBUG->append(text);

The " contains " actually accepts reg expression and string too , so I am not sure how
to tell the difference.
But it does what I want it to do.

Salvatore Terress24-Oct-23 6:50

24-Oct-23 6:50

SOLVED

Thanks to all contributors who help to find the issue.

modified 29-Oct-23 10:49am.

k505424-Oct-23 7:01

24-Oct-23 7:01

At a guess, I would bet that textEditPtr_DEBUG may not be a valid object. In brief:

C++

QTextEdit *textEditPtr_DEBUG = MWCCF->centralWidget()->findChild<QTextEdit *>("textEdit_2");
if (textEditPtr_DEBUG) {
   // textEditPtr_DEBUG is valid here
} else {
   // textEditPtr_DEBUG is not valid here
   // and we don't do anything to create a valid object ...
}
// At this point, if the else branch was followed, above then do not
// have a valid textEditPtr_DEBUG object  ...
textEditPtr_DEBUG->append(text);  //crashes as noted above

Keep Calm and Carry On

Dave Kreskowiak24-Oct-23 7:10

Dave Kreskowiak

24-Oct-23 7:10

Well, it's pretty obvious this call:

C++

QTextEdit *textEditPtr_DEBUG = MWCCF->centralWidget()->findChild<QTextEdit *>("textEdit_2");

didn't find and return the object you thought it did.

Whatever "textEdit_2" is either doesn't exist or it's not in the container you think it is and are telling the code it's in.

I know you're saying "OK here", but is it really? Put a breakpoint on the if statement right above that and run the code under the debugger. When it breaks, hover the mouse over textEditptr_DEBUG and see if it actually has a value that isn't a bunch of zeros and points to the actual object you think it does.

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

Message Closed

24-Oct-23 8:15

24-Oct-23 8:15

Message Closed

modified 26-Oct-23 12:36pm.

Dave Kreskowiak24-Oct-23 9:00

Dave Kreskowiak

24-Oct-23 9:00

Hell if I know. I haven't C++'d in about 15 years and I don't do Qt.

The process of checking return values for exactly what you expect them to be is just universal.

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

Richard MacCutchan24-Oct-23 22:12

Richard MacCutchan

24-Oct-23 22:12

The code, and the problem, is quite clear.

C++

  1  QTextEdit *textEditPtr_DEBUG = MWCCF->centralWidget()->findChild<QTextEdit *>("textEdit_2");
  2  if (textEditPtr_DEBUG)
  3  {
  4      text = " Found textEdit ";   OK here
  5      qDebug() << text;
  6      textEditPtr_DEBUG->append(text);
  7  
  8      text = " DEBUG START  DEBUG trace with textEdit_2" ;
  9      qDebug() << text;
 10      textEditPtr_DEBUG->append(text);
 11  }
 12  else
 13  {
 14      text = "Did not find any QTextEdit";
 15      qDebug() << text;
 16  }
 17  // ?? what why ??
 18  text = " DEBUG START  DEBUG trace with textEdit_2" ;
 19  textEditPtr_DEBUG->append(text);     crash -  null pointer here ??

At line 1 you (try to) create a pointer to some object.
At line 2 you test if that object is NULL, and if it is not, then you execute lines 4 to 10
If the object is NULL, then you skip to line 14
But then at line 19 you try to use a pointer which you may already have determined is NULL.

Unfortunately the debug output you have shown above does not match that code, so I am making some assumptions here.

[edit]
Also it does not help you to have the same debug message in two different places.
[/edit]

modified 25-Oct-23 5:13am.

CPallini24-Oct-23 22:38

CPallini

24-Oct-23 22:38

Pretty good assumptions, I believe.

"In testa che avete, Signor di Ceprano?"
-- Rigoletto

jschell25-Oct-23 4:44

jschell

25-Oct-23 4:44

Richard MacCutchan wrote:
If the object is NULL, then you skip to line 14

The OP shows the posted output. For example the following line.

" Sucess Found textEdit "

So line 5 is being executed (and the other lines in that block by the rest of the output.)

Of course the code is still wrong if the null pointer does show up.

Richard MacCutchan wrote:
the debug output you have shown above does not match that code

Perhaps that is the actual problem. They think they are running the code shown but the code being executed is different. I have had that happen to me. Often enough that I probably do compiles, cleans and builds far more often than is needed.

Regular expression error ?

Richard MacCutchan25-Oct-23 4:50

Richard MacCutchan

25-Oct-23 4:50

jschell wrote:
Perhaps that is the actual problem. They think they are running the code shown but the code being executed is different.

Given who I suspect is asking the question I am not at all surprised.

And if you look at OP's reply to Dave Kreskowiak you will see more confusion.

Salvatore Terress21-Oct-23 7:42

21-Oct-23 7:42

I am trying to extract MAC address from text, and it is failing.

Here is the debug print of the "inString" text to extract the MAC from :

"Inquiring ...\n\t98:D3:31:F8:39:33\tclock offset: 0x7c6b\tclass: 0x001f00\n"

Here is my temporary code with regular expression which must be in error, but I do not see it.

QRegularExpression re(" [^\x00-\x7F]+\\ *(?:[^\x00-\x7F]| )*");
        QRegularExpressionMatch match = re.match(inString);


         if (match.hasMatch()) {
            text = " Has match ";
            QStringList result = match.capturedTexts();
            text += result.at(0);    // test show only first

         }
         else
         {
            text = " NO match found ";
         }

 qDebug() << text;

Here is "run time error " , I am not sure why " invalid object" .

Does it mean my regular expression is incorrect ?

QRegularExpressionPrivate::doMatch(): called on an invalid QRegularExpression object
" NO match found "

If additional info would help, please ask.

Help analyzing the expression would be also greatly appreciated.

Thanks

Richard Andrew x6421-Oct-23 7:50

Richard Andrew x64

21-Oct-23 7:50

You can validate your regex at any number of sites that do that sort of thing. That would help you determine if the problem is the regex itself, or the QRegularExpression object.

The difficult we do right away...
...the impossible takes slightly longer.

Richard Andrew x6421-Oct-23 8:12

Richard Andrew x64

21-Oct-23 8:12

I can see one thing wrong with the expression right off the bat.

You're trying to match hexadecimal characters from 00 to FF, but the range you specify is only 00 to 7F.

The difficult we do right away...
...the impossible takes slightly longer.

Salvatore Terress21-Oct-23 8:58

21-Oct-23 8:58

Yes, I found that error too. It still fails. I am going t0 verify the expression using on one of the test sites...

Salvatore Terress22-Oct-23 6:42

22-Oct-23 6:42

Mrs Google found this

Regex.ai - Artificial Intelligence Regular Expression Generator[^]

Now for questions :
It is unclear how to select multiple entries from the text AKA highlight singe entry works ,
now to to select another part - dedicated by bold ?

Bold text
Devices:\n\thci0\t00:15:83:15:A2:CB\n

For old fart the text is too small - is there a way to make it bigger or do I have to tell Ubuntu ?

David Crow23-Oct-23 2:12

David Crow

23-Oct-23 2:12

Another option would be something like:

int pos1 = index of first \t in inString;
int pos2 = index of second \t in inString;
int length = pos2 - pos1;
string MAC = inString.substring(pos1, length);

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Salvatore Terress23-Oct-23 5:10

23-Oct-23 5:10

Yes, this just proves there is more than one way to skin a cat...
I did checked two AI regular expression generators and they came up with two solutions..
One pretty goofy.
My current preference to match MAC address is :
([0-F]{2}[:]){5}[0-F]{2})
it "finds" the address, but also finds a single two character in it.
The interesting part , the [0-F] apparently searches for characters between ASCII O and F - it does not search for digits. ( My opinion)

k505423-Oct-23 5:50

23-Oct-23 5:50

The range [0-F] includes the characters :;<=>@, and does not include lowercase letetrs. You're better off either with [0-9a-fA-F]. Alternatively, if your regex engine has character classes then you could use ([[:xdigit:]]{2}[:]){5}[[:xdigit:]]{2} I'm not sure you need to specify the colon as a match set, unless regex treats them as special characters.

Keep Calm and Carry On

Salvatore Terress24-Oct-23 5:01

24-Oct-23 5:01

Thanks, as long as the entry is characters , not numbers, it makes sense.
Since the MAC address "hex numbers" is capitals I do not need [a-f ].
You have a good point - I'll try to delete [:] - in theory it should work.

k505424-Oct-23 6:00

24-Oct-23 6:00

Salvatore Terress wrote:
Thanks, as long as the entry is characters , not numbers, it makes sense.

Why would they not be characters? You seem to be reading input from another command, so it should always be characters.

Salvatore Terress wrote:
Since the MAC address "hex numbers" is capitals I do not need [a-f ].

That depends. Can you guarantee that you'll always get upper case hex digits? Under linux, the arp commands uses lower case letters for the MAC address. Others might as well

Salvatore Terress wrote:
You have a good point - I'll try to delete [:] - in theory it should work.

It should. But as noted above, it would depend on where you're getting your input from. Under Windows, if you run ipconfig /all you get the Mac address separated by dashes e.g. "00-4B-35-30-35-34", so you may need to allow for that too.

Keep Calm and Carry On

RedDk24-Oct-23 8:01

RedDk

24-Oct-23 8:01

Salvatore Terress wrote:
([0-F]{2}[:]){5}[0-F]{2})

Should be:

([0-F]{2}[:]){5}[0-F]{2}

modified 25-Oct-23 2:01am.

How to pass parameter (pointer) to function ?

jschell23-Oct-23 5:16

jschell

23-Oct-23 5:16

Google seems to return regular expressions to validate a mac address. Not to mention explaining forms that might be less than obvious.

mac address regular expression

Other than that the square brackets are used for character matching. Single character. Best I can tell you seem to be trying to match a sequence of characters (2 digit hex.)

Salvatore Terress19-Oct-23 14:50

Re: How to pass parameter (pointer) to function ?

19-Oct-23 14:50

What is a correct way to pass parameter / variable to function ?

The attached snippet writes text to the GUI object and it is done in object constructor.
My task is to pass ui->textEdit_2 to object function so it can be processed OUTSIDE constructor

ui->setupUi(this);

 text = "Constructor ";
 ui->textEdit_2->append(text);

 text = " Initialize DEBUG trace ";
 ui->textEdit_2->append(text);

private:
public:
    Ui::MainWindow_C_CODE_FORM *ui;

Here is my test function declaration:

QString ShowText(QString text, QTextEdit *textEDIT );

I have tried several ways to access the function, but I am obviously "doing it wrong".

PS
I you cannot help "as is " , please, do not complain - it would work better
if you ask what is missing instead.
Thank you very much .

k505419-Oct-23 17:16