Program crashes when global variable included.

[jbbb]

@mrjj Hi, ! cant remove my parameters as it is a signal and slot.

At my main mindow(signal):

void MainWindow::themereadData(const QByteArray &data)
{
      m_themewidget->generateRandomData(data);
}

hence when at ThemeWidget.cpp:

DataTable ThemeWidget::generateRandomData(const QByteArray &data)

my function must have &data for the data to enter this .cpp

Not quite sure how it can be done although i understand your point about the members.

[mrjj]

@jbbb

Ah ok. well then it needs the parameter.
I think the code confused me as you seemed to send a member as parameter but
now it makes sense.

So did you find the actual crashing ?

[jbbb]

@mrjj There is a segmentation fault when i input a global variable into the function below.

DataTable ThemeWidget::generateRandomData(const QByteArray &data)
{
    DataTable dataTable;
    QByteArray testdata = data;
     qDebug() << testdata << "hi";
    QString headerbyte = testdata.left(10);
    testdata.remove(0,10);
    // generate testdata
    int listCount = 1;
    for (int i(0); i < listCount; i++) {
        DataList dataList;
        float yValue(0);
        int count(0);
        QString datavalue;
        QString checksign;
        for (int j(0); j<136; j++)
        {
            testdata.remove(0,1);
            checksign = testdata.left(1);
            if (checksign == "-"){
                datavalue = testdata.left(7);
                testdata.remove(0,7);
            }
            else{
                datavalue = testdata.left(6);
                testdata.remove(0,6);
            }
            yValue = datavalue.toFloat();
            QPointF value(count, yValue);
            count++;
            dataList << Data(value);
        }
        dataTable << dataList;
    }
    return dataTable;
}

the reason why i will need a global variable is because of:
m_dataTable(generateRandomData(m_data))

As this function is a return function, I will need a variable to input to the function. However, &data in my function is my actual data. Hence, I wanted to use m_data to be pointing to data so that m_data will have the same data stored.

I am not sure of the reason why there will be a fault. Hope you can enlighten me!

[mrjj]

@jbbb

Well global variables should normally be avoided as it gives a spaghetti design but
it should not crash as such.

Do notice that no Qt-based (QObject) class can be used as global variable. Its forbidden.

So what type was your global variable?

and why did you need it to be global ?

[jbbb]

@mrjj

#include "themewidget.h"
#include "ui_themewidget.h"
#include "tcpserver.h"

#include <iostream>
#include <QtCharts/QChartView>
#include <QtCharts/QLineSeries>
#include <QtCharts/QLegend>
#include <QtWidgets/QGridLayout>
#include <QtWidgets/QFormLayout>
#include <QtWidgets/QComboBox>
#include <QtWidgets/QSpinBox>
#include <QtWidgets/QCheckBox>
#include <QtWidgets/QGroupBox>
#include <QtWidgets/QLabel>
#include <QtCore/QRandomGenerator>
#include <QtCharts/QBarCategoryAxis>
#include <QtWidgets/QApplication>
#include <QtCharts/QValueAxis>

ThemeWidget::ThemeWidget(QWidget *parent) :
    QWidget(parent),
    m_listCount(1),
    m_valueMax(136),
    m_valueCount(0.5),   
    m_dataTable(generateRandomData(m_data)),
    m_dataTable1(generateDataTest()),
    m_ui(new Ui_ThemeWidgetForm)
    //m_dataTable(generateRandomData(m_listCount, m_valueMax, m_valueCount)),
{
    m_ui->setupUi(this);
    //create charts
    QChartView *chartView;

ThemeWidget::~ThemeWidget()
{
    delete m_ui;
}
DataTable ThemeWidget::generateRandomData(const QByteArray &data, QByteArray*pData)
{
    DataTable dataTable;
     QByteArray testdata = data;
    m_data = testdata;
    QString headerbyte = testdata.left(10);
    testdata.remove(0,10);
    // generate testdata
    int listCount = 1;
    for (int i(0); i < listCount; i++) {
        DataList dataList;
        float yValue(0);
        int count(0);
        QString datavalue;
        QString checksign;
        for (int j(0); j<136; j++)
        {
            testdata.remove(0,1);
            checksign = testdata.left(1);
            if (checksign == "-"){
                datavalue = testdata.left(7);
                testdata.remove(0,7);
            }
            else{
                datavalue = testdata.left(6);
                testdata.remove(0,6);
            }
            yValue = datavalue.toFloat();
            QPointF value(count, yValue);
            count++;
            dataList << Data(value);
        }
        dataTable << dataList;
    }
    return dataTable;
}

This is the codes that will create a segmentation fault. My global variable is
QByteArray m_data that is initialized in the .header file.

m_data = testdata;

this is so that m_data for m_dataTable(generateRandomData(m_data)) will have the same data other wise m_data will be empty.

[mrjj]

@jbbb

well it might be a dangling pointer maybe ?

You can find out with the debugger.

Place a break point on generateRandomData and then
use F10 to spep over each line and see what lines it crashes at.

[J.Hilk]

@jbbb said in Program crashes when global variable included.:

My global variable is
QByteArray m_data that is initialized in the .header file.

m_data is not a global variable, its member one

private:
    int m_listCount;
    int m_valueMax;
    float m_valueCount;
    QList<QChartView *> m_charts;
    DataTable m_dataTable;
    QByteArray m_data;

[jbbb]

@J-Hilk how do i set the global variable instead? not in .h file?

[jbbb]

@mrjj it crashes at m_data = testdata;

and this pops out:

QByteArray &QByteArray::operator=(const QByteArray & other) Q_DECL_NOTHROW
{
    other.d->ref.ref();
    if (!d->ref.deref())
        Data::deallocate(d);
    d = other.d;
    return *this;
}

any idea what this means?

[Christian Ehrlicher]

@jbbb said in Program crashes when global variable included.:

any idea what this means?

Take a look at the stacktrace to see where it comes from (as already said in my first post).
I would guess the this pointer is a nullptr.