Getting segmentation fault when using Ui_LoginScreen().lineEdit->text();

volkish

Hello I am stuck and cannot continue further.

My application is about to read a database and then compare the input from a login interface where the user types his password and username. I have so far designed the login interface but I keep getting this segmentation fault whenever I try to run the code? I just want to compare the input with the values from the database. Why do I get this segmentation error and how can I solve it ?
Here is my code

  #include "LoginScreen.h"
  #include <QApplication>
  #include <QMessageBox>


  LoginScreen::LoginScreen(){

    widget.setupUi(this);
    connect(widget.pushButton, SIGNAL(clicked()),this, SLOT(clickedSlot()));

  }

  LoginScreen::~LoginScreen(){}

   void LoginScreen::clickedSlot(){
  
   QMessageBox msgBox;
   QString usernameFromInterface,passwordFromInterface;
    
   usernameFromInterface = Ui_LoginScreen().lineEdit->text();//ERROR OCCURS HERE
   }

dheerendra

Your ui_loginscreen object may be null. Check it.

volkish

How do I check if it is null ? This is the body that is generated. Should I declare it somewhere in the main maybe??
[code]

        /********************************************************************************
        ** Form generated from reading UI file 'LoginScreen.ui'
        **
        ** Created by: Qt User Interface Compiler version 5.5.1
        **
        ** WARNING! All changes made in this file will be lost when recompiling UI file!
        ********************************************************************************/

        #ifndef UI_LOGINSCREEN_H
        #define UI_LOGINSCREEN_H

        #include <QtCore/QVariant>
        #include <QtWidgets/QAction>
        #include <QtWidgets/QApplication>
        #include <QtWidgets/QButtonGroup>
        #include <QtWidgets/QDialog>
        #include <QtWidgets/QHeaderView>
        #include <QtWidgets/QLabel>
        #include <QtWidgets/QLineEdit>
        #include <QtWidgets/QPushButton>

        QT_BEGIN_NAMESPACE

        class Ui_LoginScreen
        {
        public:
            QLineEdit *lineEdit;
            QLineEdit *lineEdit_2;
            QLabel *label;
            QLabel *label_2;
            QPushButton *pushButton;
            QLabel *label_3;

            void setupUi(QDialog *LoginScreen)
            {
                if (LoginScreen->objectName().isEmpty())
                    LoginScreen->setObjectName(QStringLiteral("LoginScreen"));
                LoginScreen->resize(693, 429);
                lineEdit = new QLineEdit(LoginScreen);
                lineEdit->setObjectName(QStringLiteral("lineEdit"));
                lineEdit->setGeometry(QRect(270, 120, 113, 20));
                lineEdit_2 = new QLineEdit(LoginScreen);
                lineEdit_2->setObjectName(QStringLiteral("lineEdit_2"));
                lineEdit_2->setGeometry(QRect(270, 170, 113, 20));
                lineEdit_2->setEchoMode(QLineEdit::Password);
                label = new QLabel(LoginScreen);
                label->setObjectName(QStringLiteral("label"));
                label->setGeometry(QRect(270, 100, 47, 13));
                label_2 = new QLabel(LoginScreen);
                label_2->setObjectName(QStringLiteral("label_2"));
                label_2->setGeometry(QRect(270, 150, 47, 13));
                pushButton = new QPushButton(LoginScreen);
                pushButton->setObjectName(QStringLiteral("pushButton"));
                pushButton->setGeometry(QRect(290, 210, 75, 23));
                pushButton->setCheckable(true);
                label_3 = new QLabel(LoginScreen);
                label_3->setObjectName(QStringLiteral("label_3"));
                label_3->setGeometry(QRect(270, 30, 141, 61));
                label_3->setTextFormat(Qt::RichText);
                label_3->setMargin(5);
                label_3->setIndent(5);

                retranslateUi(LoginScreen);
        
                QMetaObject::connectSlotsByName(LoginScreen);
            } // setupUi

            void retranslateUi(QDialog *LoginScreen)
            {
                LoginScreen->setWindowTitle(QApplication::translate("LoginScreen", "LoginScreen", 0));
                label->setText(QApplication::translate("LoginScreen", "Username", 0));
                label_2->setText(QApplication::translate("LoginScreen", "Password", 0));
                pushButton->setText(QApplication::translate("LoginScreen", "Ok", 0));
                label_3->setText(QApplication::translate("LoginScreen", "Welcome to SEP", 0));
            } // retranslateUi
        
        };

        namespace Ui {
            class LoginScreen: public Ui_LoginScreen {};
        } // namespace Ui

        QT_END_NAMESPACE

        #endif // UI_LOGINSCREEN_H

SGaist

Hi,

Because you're code is wrong. you are instantiating an object of type Ui_LoginScreen without initialising it. But even if you did you would not get the value you expect.

I take it that your widget variable type is Ui_LoginScreen, correct ? If so, you should use it to retrieve the text from the lineEdit widget.