Using static variables in programs

tomy

Hi,

Please take a look at this shortened version of the real app. I built this program just to follow and solve the issue in a simpler way. How to use a static variable. well, of course, my purpose is to prevent various objects to have a copy of that.

#ifndef TEST1_H
#define TEST1_H
#include <QDialog>

class QLineEdit;
class QPushButton;

class test1 : public QDialog
{
    Q_OBJECT

public:
    test1(QWidget* parent = 0);

private slots:
    void show_clicked();

private:
    static int i;
    QLineEdit* line;
    QPushButton* show_number;
    QPushButton* quit;

};

#endif // TEST1_H

#include <QtWidgets>
#include "test1.h"

test1::test1(QWidget* parent)
    : QDialog(parent)
{
  i = 5;
 line = new QLineEdit;
  show_number = new QPushButton(tr("show"));
  quit = new QPushButton(tr("Quit"));

  connect(show_number, SIGNAL(clicked(bool)),
          this, SLOT(show_clicked()));
  connect(quit, SIGNAL(clicked(bool)), this, SLOT(close));

  QVBoxLayout* layout = new QVBoxLayout();
  layout->addWidget(line);
  layout->addWidget(show_number);
  layout->addWidget(quit);
  setLayout(layout);
}

//**********************************

void test1::show_clicked()
{
  line->setText(QString::number(i));
}

#include<QApplication>
#include "test1.h"

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);
    test1* t1 = new test1;
    t1->show();
    return app.exec();
}

When I run the code I get 3 errors:

error: undefined reference to `test1::i'

error: error: ld returned 1 exit status

beecksche

Hi @tomy ,
you have to define them "outside" again:

Add in your .cpp:

int test1::i = 0;

test1::test1(QWidget* parent)
    : QDialog(parent) { ... }

tomy

This post is deleted!

tomy

@beecksche
Thank you. It was solved.