why i am getting this error: use of undeclared identifier 'MainWindow' ?

Qt embedded developer

I have created simple c++ based qt project.

I am using QMake version 3.1
Using Qt version 5.12.8 in /usr/lib/x86_64-linux-gnu

by default kit is coming like desktop

but i want to make simple widget application uisng qt c++.

so for that how to add kit that will not show below error.
but what i need

when i am running the project i am getting below error:

/home/mangal/JAYMOGAL/MYFIRST/part1/mainwindow.cpp:5: error: use of undeclared identifier 'MainWindow'

Christian Ehrlicher

Because you did not declare a class named 'MainWindow' maybe?

Qt embedded developer

@Christian-Ehrlicher no this is not the problem because by default while we make new project this by default added by qt. i think this problem is related to kit. and i don't know how to resolve kit related problem. i don't know which kit i need to add for my simple c++ qt project .i have doubt is that in .pro file

that by default conains

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

JonB

@Qt-embedded-developer
.pro file has nothing to do with it. The error says it is on line #5 of the .cpp file. Why don't you look at what the first 5 lines are?

Qt embedded developer

@JonB for your reference the code for .cpp file is

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

}

MainWindow::~MainWindow()
{
    delete ui;
}

so just tell me what you want to say about my line 5 problem. i want to understand it. i want to know the solution of it also.

JonB

@Qt-embedded-developer said in why i am getting this error: use of undeclared identifier 'MainWindow' ?:

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>

MainWindow::MainWindow(QWidget *parent)

So none of the #included files defines MainWindow. Only you have those files. If you want to understand why have a look in them. Maybe you need to force build to regenerate ui_mainwindow.h. Maybe you renamed the class in the .ui file. Maybe your mainwindow.h file is wrong.

Qt embedded developer

@JonB i have not manually created any file. this is by default file added by qt

for your reference my mainwindow.h file contain this class defination

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

JonB

@Qt-embedded-developer
That looks as I would expect. So far I cannot see why you would get the error you reported. Assume there were no other errors reported.

What about the generated ui_mainwindow.h file from the .ui file, which is in the compilation output (usually Build-...) directory? Force a clean build; you could just delete all the files in that output (not your sources!) directory. Though that should not be the issue....

Christian Ehrlicher

There is another mainwindow.h somewhere around which the compiler is using - seeing the other posts about the include path mess this is at least a very good option here...

JonB

@Christian-Ehrlicher Ooohhhh! :)

Qt embedded developer

@JonB i have deleted the all the files from output directory.

my compile output is:

10:55:52: Running steps for project part1...
10:55:52: Starting: "/usr/bin/x86_64-linux-gnu-qmake" /home/mangal/JAYMOGAL/MYFIRST/part1/part1.pro -spec linux-g++-64 CONFIG+=debug CONFIG+=qml_debug
10:55:52: The process "/usr/bin/x86_64-linux-gnu-qmake" exited normally.
10:55:52: Starting: "/usr/bin/make" -f /home/mangal/JAYMOGAL/MYFIRST/build-part1-Qt_5_12_8_System-Debug/Makefile qmake_all
make: Nothing to be done for 'qmake_all'.
10:55:52: The process "/usr/bin/make" exited normally.
10:55:52: Starting: "/usr/bin/make" -j2
/usr/lib/qt5/bin/uic ../part1/mainwindow.ui -o ui_mainwindow.h
x86_64-linux-gnu-g++ -c -m64 -pipe -g -std=gnu++11 -Wall -W -D_REENTRANT -fPIC -DQT_DEPRECATED_WARNINGS -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../part1 -I. -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/x86_64-linux-gnu/qt5/QtWidgets -isystem /usr/include/x86_64-linux-gnu/qt5/QtGui -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -I. -I. -I/usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++-64 -o main.o ../part1/main.cpp
x86_64-linux-gnu-g++ -m64 -pipe -g -std=gnu++11 -Wall -W -dM -E -o moc_predefs.h /usr/lib/x86_64-linux-gnu/qt5/mkspecs/features/data/dummy.cpp
x86_64-linux-gnu-g++ -c -m64 -pipe -g -std=gnu++11 -Wall -W -D_REENTRANT -fPIC -DQT_DEPRECATED_WARNINGS -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../part1 -I. -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/x86_64-linux-gnu/qt5/QtWidgets -isystem /usr/include/x86_64-linux-gnu/qt5/QtGui -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -I. -I. -I/usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++-64 -o mainwindow.o ../part1/mainwindow.cpp
/usr/lib/qt5/bin/moc -DQT_DEPRECATED_WARNINGS -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB --include /home/mangal/JAYMOGAL/MYFIRST/build-part1-Qt_5_12_8_System-Debug/moc_predefs.h -I/usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++-64 -I/home/mangal/JAYMOGAL/MYFIRST/part1 -I/usr/include/x86_64-linux-gnu/qt5 -I/usr/include/x86_64-linux-gnu/qt5/QtWidgets -I/usr/include/x86_64-linux-gnu/qt5/QtGui -I/usr/include/x86_64-linux-gnu/qt5/QtCore -I. -I/usr/include/c++/9 -I/usr/include/x86_64-linux-gnu/c++/9 -I/usr/include/c++/9/backward -I/usr/lib/gcc/x86_64-linux-gnu/9/include -I/usr/local/include -I/usr/include/x86_64-linux-gnu -I/usr/include ../part1/mainwindow.h -o moc_mainwindow.cpp
x86_64-linux-gnu-g++ -c -m64 -pipe -g -std=gnu++11 -Wall -W -D_REENTRANT -fPIC -DQT_DEPRECATED_WARNINGS -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../part1 -I. -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/x86_64-linux-gnu/qt5/QtWidgets -isystem /usr/include/x86_64-linux-gnu/qt5/QtGui -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -I. -I. -I/usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++-64 -o moc_mainwindow.o moc_mainwindow.cpp
x86_64-linux-gnu-g++ -m64 -o part1 main.o mainwindow.o moc_mainwindow.o   -L/usr/X11R6/lib64 /usr/lib/x86_64-linux-gnu/libQt5Widgets.so /usr/lib/x86_64-linux-gnu/libQt5Gui.so /usr/lib/x86_64-linux-gnu/libQt5Core.so /usr/lib/x86_64-linux-gnu/libGL.so -lpthread   
10:55:59: The process "/usr/bin/make" exited normally.
10:55:59: Elapsed time: 00:07.

but still i get this warning in issue window:
mainwindow.h:10: error: expected class name

JonB

@Qt-embedded-developer said in why i am getting this error: use of undeclared identifier 'MainWindow' ?:

but still i get this warning in issue window:
mainwindow.h:10: error: expected class name

I don't know what the "issue" window is, maybe this is code model warning not from compiler?

Qt embedded developer

@JonB what to do to stop code model warning in qt creator ?

jsulm

@Qt-embedded-developer said in why i am getting this error: use of undeclared identifier 'MainWindow' ?:

what to do to stop code model warning in qt creator ?

Disable the Clang plug-in (in Help/About Plugins...)

Qt embedded developer

@jsulm when i am disable it my building of project process not get stop. it continuously running.

jsulm

@Qt-embedded-developer Clang plug-in has actually nothing to do with the build.
Try complete rebuild: delete build folder, run qmake and then build.