Qt6 QMake

Jiej

Hi,

I've just installed Qt6 on Ubuntu using the command

sudo apt install qt6-base-dev

and when I create a Makefile with QMake6 for a simple C++ project that opens a QWidget, the compilation fails because it can't find QApplication header.

The command executed by the makefile is

g++ -c -pipe -O2 -Wall -Wextra -fPIC -D_REENTRANT -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -I. -I. -I/usr/include/x86_64-linux-gnu/qt6 -I/usr/include/x86_64-linux-gnu/qt6/QtGui -I/usr/include/x86_64-linux-gnu/qt6/QtCore -I. -I/usr/lib/x86_64-linux-gnu/qt6/mkspecs/linux-g++ -o main.o main.cpp

How to solve this ?

Thank you

Christian Ehrlicher

When you want to use widgets, you should specify it in your pro file.
See e.g. https://doc.qt.io/qt-6/qlabel.html

Jiej

@Christian-Ehrlicher Thank you for your reply.
I think I did specify it in my .pro file but the compiler still can't find it.

My project file is this one :

TEMPLATE = app
TARGET = main
QT += core gui widgets
CONFIG += c++11

SOURCES += main.cpp

Christian Ehrlicher

Your compiler output does not match the pro file. Rerun qmake on a clean build dir

Jiej

@Christian-Ehrlicher It worked.
Thank you.
This time QMake generated a different project file :

######################################################################
# Automatically generated by qmake (3.1) Sun Dec 8 19:29:47 2024
######################################################################

TEMPLATE = app
TARGET = Qt_First_Project
INCLUDEPATH += .

# You can make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# Please consult the documentation of the deprecated API in order to know
# how to port your code away from it.
# 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

# Input
SOURCES += main.cpp

I added QT += gui core widgets and the compilation was successful.