The application crashes after 3 seconds.I'm writing a task manager in qt with a database,.

Torch

Compile output

21:48:24: Starting C:\Users\Julia\Documents\qtprojects\taskman\build\Desktop_Qt_6_7_1_MinGW_64_bit-Debug\debug\taskman.exe...
Application started
Database: connection ok
Error adding task: "Parameter count mismatch"
Failed to add Task 1
Error adding task: "Parameter count mismatch"
Failed to add Task 2
Printing tasks...
Finished printing tasks.
Starting event loop
21:48:28: C:\Users\Julia\Documents\qtprojects\taskman\build\Desktop_Qt_6_7_1_MinGW_64_bit-Debug\debug\taskman.exe exited with code 0

Taskman.pro

QT += core gui sql

CONFIG += c++17

greaterThan(QT_MAJOR_VERSION, 5): QT += widgets

TARGET = taskman
TEMPLATE = app

SOURCES += main.cpp \
           Task.cpp \
           TaskManager.cpp \
           DatabaseManager.cpp

HEADERS += Task.h \
           TaskManager.h \
           DatabaseManager.h

main.cpp

#include <QApplication>
#include "TaskManager.h"
#include "DatabaseManager.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    DatabaseManager dbManager("tasks.db");
    TaskManager taskManager(&dbManager);

    taskManager.show();

    return app.exec();
}

Task.h

#ifndef TASK_H
#define TASK_H

#include <QString>
#include <QDate>

class Task
{
public:
    Task(const QString &title, const QString &description, const QDate &dueDate);

    QString getTitle() const;
    QString getDescription() const;
    QDate getDueDate() const;

private:
    QString title;
    QString description;
    QDate dueDate;
};

#endif // TASK_H


Task.cpp

#include "Task.h"

Task::Task(const QString &title, const QString &description, const QDate &dueDate)
    : title(title), description(description), dueDate(dueDate)
{
}

QString Task::getTitle() const
{
    return title;
}

QString Task::getDescription() const
{
    return description;
}

QDate Task::getDueDate() const
{
    return dueDate;
}

Taskmanager.h

#ifndef TASKMANAGER_H
#define TASKMANAGER_H

#include <QWidget>
#include <QVBoxLayout>
#include <QLabel>
#include <QPushButton>
#include "DatabaseManager.h"

class TaskManager : public QWidget
{
    Q_OBJECT

public:
    TaskManager(DatabaseManager *dbManager, QWidget *parent = nullptr);

private:
    DatabaseManager *dbManager;
    QVBoxLayout *layout;
    QLabel *titleLabel;
    QLabel *descriptionLabel;
    QLabel *dueDateLabel;
    QPushButton *closeButton;

private slots:
    void onCloseButtonClicked();
};

#endif // TASKMANAGER_H

Taskmanager.cpp

#include "TaskManager.h"
#include <QVBoxLayout>
#include <QLabel>
#include <QPushButton>

TaskManager::TaskManager(DatabaseManager *dbManager, QWidget *parent)
    : QWidget(parent), dbManager(dbManager)
{
    layout = new QVBoxLayout(this);

    titleLabel = new QLabel("Title", this);
    descriptionLabel = new QLabel("Description", this);
    dueDateLabel = new QLabel("Due Date", this);
    closeButton = new QPushButton("Close", this);

    layout->addWidget(titleLabel);
    layout->addWidget(descriptionLabel);
    layout->addWidget(dueDateLabel);
    layout->addWidget(closeButton);

    connect(closeButton, &QPushButton::clicked, this, &TaskManager::onCloseButtonClicked);
}

void TaskManager::onCloseButtonClicked()
{
    close();
}

Database.h

#ifndef DATABASEMANAGER_H
#define DATABASEMANAGER_H

#include <QString>
#include <QVector>
#include "Task.h"

class DatabaseManager
{
public:
    DatabaseManager(const QString &path);
    QVector<Task> getAllTasks() const;

private:
    QString dbPath;
};

#endif // DATABASEMANAGER_H

Database.cpp

#include "DatabaseManager.h"
#include <QSqlDatabase>
#include <QSqlQuery>
#include <QSqlError>
#include <QVariant>

DatabaseManager::DatabaseManager(const QString &path)
    : dbPath(path)
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName(dbPath);

    if (!db.open()) {
        qDebug() << "Error: connection with database failed";
    } else {
        qDebug() << "Database: connection ok";
    }
}

QVector<Task> DatabaseManager::getAllTasks() const
{
    QVector<Task> tasks;
    QSqlQuery query("SELECT title, description, due_date FROM tasks");

    while (query.next()) {
        QString title = query.value(0).toString();
        QString description = query.value(1).toString();
        QDate dueDate = query.value(2).toDate();
        tasks.append(Task(title, description, dueDate));
    }

    return tasks;
}

jsulm

@Torch So, what does stack trace in debugger say after the crash?
Debugging is the first thing to do if the application crashes...

Torch

@jsulm

20:49:38: Running steps for project taskman...
20:49:38: Configuration unchanged, skipping qmake step.
20:49:38: Starting: "C:\Qt\Tools\mingw1120_64\bin\mingw32-make.exe" -j4
C:/Qt/Tools/mingw1120_64/bin/mingw32-make -f Makefile.Debug
mingw32-make[1]: Entering directory 'C:/Users/Julia/Documents/qtprojects/taskman/build/Desktop_Qt_6_7_1_MinGW_64_bit-Debug'
g++ -c -fno-keep-inline-dllexport -g -Wall -Wextra -Wextra -fexceptions -mthreads -DUNICODE -D_UNICODE -DWIN32 -DMINGW_HAS_SECURE_API=1 -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_SQL_LIB -DQT_CORE_LIB -DQT_NEEDS_QMAIN -I../../../taskman2 -I. -IC:/Qt/6.7.1/mingw_64/include -IC:/Qt/6.7.1/mingw_64/include/QtWidgets -IC:/Qt/6.7.1/mingw_64/include/QtGui -IC:/Qt/6.7.1/mingw_64/include/QtSql -IC:/Qt/6.7.1/mingw_64/include/QtCore -Idebug -I/include -IC:/Qt/6.7.1/mingw_64/mkspecs/win32-g++  -o debug\main.o ..\..\..\taskman2\main.cpp
g++ -c -fno-keep-inline-dllexport -g -Wall -Wextra -Wextra -fexceptions -mthreads -DUNICODE -D_UNICODE -DWIN32 -DMINGW_HAS_SECURE_API=1 -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_SQL_LIB -DQT_CORE_LIB -DQT_NEEDS_QMAIN -I../../../taskman2 -I. -IC:/Qt/6.7.1/mingw_64/include -IC:/Qt/6.7.1/mingw_64/include/QtWidgets -IC:/Qt/6.7.1/mingw_64/include/QtGui -IC:/Qt/6.7.1/mingw_64/include/QtSql -IC:/Qt/6.7.1/mingw_64/include/QtCore -Idebug -I/include -IC:/Qt/6.7.1/mingw_64/mkspecs/win32-g++  -o debug\TaskManager.o ..\..\..\taskman2\TaskManager.cpp
g++ -c -fno-keep-inline-dllexport -g -Wall -Wextra -Wextra -fexceptions -mthreads -DUNICODE -D_UNICODE -DWIN32 -DMINGW_HAS_SECURE_API=1 -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_SQL_LIB -DQT_CORE_LIB -DQT_NEEDS_QMAIN -I../../../taskman2 -I. -IC:/Qt/6.7.1/mingw_64/include -IC:/Qt/6.7.1/mingw_64/include/QtWidgets -IC:/Qt/6.7.1/mingw_64/include/QtGui -IC:/Qt/6.7.1/mingw_64/include/QtSql -IC:/Qt/6.7.1/mingw_64/include/QtCore -Idebug -I/include -IC:/Qt/6.7.1/mingw_64/mkspecs/win32-g++  -o debug\DatabaseManager.o ..\..\..\taskman2\DatabaseManager.cpp
g++ -Wl,-subsystem,windows -mthreads -o debug\taskman.exe debug/main.o debug/Task.o debug/TaskManager.o debug/DatabaseManager.o C:\Qt\6.7.1\mingw_64\lib\libQt6Widgets.a C:\Qt\6.7.1\mingw_64\lib\libQt6Gui.a C:\Qt\6.7.1\mingw_64\lib\libQt6Sql.a C:\Qt\6.7.1\mingw_64\lib\libQt6Core.a -lmingw32 C:\Qt\6.7.1\mingw_64\lib\libQt6EntryPoint.a -lshell32  
mingw32-make[1]: Leaving directory 'C:/Users/Julia/Documents/qtprojects/taskman/build/Desktop_Qt_6_7_1_MinGW_64_bit-Debug'
20:50:31: The process "C:\Qt\Tools\mingw1120_64\bin\mingw32-make.exe" exited normally.
20:50:31: Elapsed time: 00:53.

Is it proper debugging? Im newbee

21:15:19: Starting C:\Users\Julia\Documents\qtprojects\taskman\build\Desktop_Qt_6_7_1_MinGW_64_bit-Debug\debug\taskman.exe...
Application started
Initializing DatabaseManager with path: "tasks.db"
Database: connection ok
Adding task: "Task 1"
Error adding task: "Parameter count mismatch"
Failed to add Task 1
Adding task: "Task 2"
Error adding task: "Parameter count mismatch"
Failed to add Task 2
Fetching tasks from database
Fetched 0 tasks
Printing tasks...
Finished printing tasks.
Starting event loop
21:15:22: C:\Users\Julia\Documents\qtprojects\taskman\build\Desktop_Qt_6_7_1_MinGW_64_bit-Debug\debug\taskman.exe exited with code 0

jsulm

@Torch said in The application crashes after 3 seconds.I'm writing a task manager in qt with a database,.:

Is it proper debugging?

No, this is build log.
Run your app in debugger (in QtCreator it is the green triangle with a bug on it in the left bottom corner).

Did you also notice the errors in the output of your application?

Error adding task: "Parameter count mismatch"
Failed to add Task 1
Error adding task: "Parameter count mismatch"
Failed to add Task 2

From where in your code are they coming?

Torch

I forgot to post here Task.cpp

#include "Task.h"

Task::Task(const QString &title, const QString &description, const QDate &dueDate)
    : title(title), description(description), dueDate(dueDate)
{
}

QString Task::getTitle() const
{
    return title;
}

QString Task::getDescription() const
{
    return description;
}

QDate Task::getDueDate() const
{
    return dueDate;
}

Later i will try debugging

Axel Spoerl

"Parameter count mismatch" comes from QSqliLiteDriver::exec(), which is probably entered when the event loop starts spinning. As the message indicates, the number of parameters to be passed to the database doesn't match up with the expected count (derived from the indexes).

Just by code-reading, there is nothing obviously crash-prone in the code.
What does stand out, though:

DatabaseManager::getAllTasks() constructs an QSqlQuery without passing a database object.
The method doesn't get called from anywhere in the posted code.

That means on the one hand, there probably is code that you don't show.
On the other hand, database errors aren't handled. That's probably the reason for the crash.

JonB

@Torch said in The application crashes after 3 seconds.I'm writing a task manager in qt with a database,.:

Adding task: "Task 1"
Error adding task: "Parameter count mismatch"
Failed to add Task 1

So don't you think this code needs showing?