Error: undefined reference to _imp_***

Question

I am getting errors like error: undefined reference to __imp__ZN12QApplicationC1ERiPPci' and error: undefined reference to __imp__ZN11QMainWindow11qt_metacastEPKc' on project build. I have tried cleaning and rebuilding but nothing has worked.

I have seen many other posts about this error, but no fix methods have worked. I am new to Qt creator, so I am probably missing something big here, but I made a widget project. Here are the files:

main.cpp

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

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

mainwindow.cpp

#include "mainwindow.h"
#include <QPushButton>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    setFixedSize(500,500);
    QPushButton myButton;
    myButton.setText("Hello world, this is a GUI app!!!");
}

MainWindow::~MainWindow()
{

}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
};

#endif // MAINWINDOW_H

myWindow.pro

#-------------------------------------------------
#
# Project created by QtCreator 2018-03-11T19:52:19
#
#-------------------------------------------------

QT       += core gui


greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = myWindow
TEMPLATE = app

# The following define makes your compiler emit warnings if you use
# any feature of Qt which has been marked as deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0
QT += sql #added because I found this to try and solve my problem, doesn't fix

SOURCES += \
        main.cpp \
        mainwindow.cpp

HEADERS += \
        mainwindow.h

My Qt version 5.10.1, OS is Windows, compiler is MinGW 64.

Answer 1

Ok, I fixed it myself, so here's what two things I messed around with:

1. Extending QWidget instead of QMainWindow
   (Pretty simple)

2. Checking my kits and using one with the correct version of MinGW - not 64 or 32 bit, it was called something completely different but still had MinGW in the name ;)

Answer 2

The fix is done by installing appropriate versions of the packages you are using. Some new code techniques can be a hard issue, so installing the right type of package can be hard but required sometimes.