How make a window with QT 6,0? - qt

Question

Hi to everyone Im beguinner with QT 6.0 Im started to practice with but I get this error message
C:\Users\blabla\Documents\Programming\VentanaPrincipal\main.cpp:6: error: undefined reference to `__imp__ZN7QWidgetC1EPS_6QFlagsIN2Qt10WindowTypeEE'
CMakeFiles/VentanaPrincipal.dir/main.cpp.obj: In function `main':
C:/Users/blabla/Documents/Programming/VentanaPrincipal/main.cpp:6: undefined reference to `__imp__ZN7QWidgetC1EPS_6QFlagsIN2Qt10WindowTypeEE'
literally this is the code what I made and As well I'm saw at https://doc.qt.io/qt-5/qtwidgets-tutorials-widgets-toplevel-example.html
#include <QCoreApplication>
#include <QtWidgets/QtWidgets>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QWidget window;
window.resize(320,240);
window.show();
return a.exec();
}

Answer 1

Based on comments to your question, your CMakeLists.txt file has this for the library requirements:
target_link_libraries(VentanaPrincipal Qt${QT_VERSION_MAJOR}::Core)
While core brings in a large chunk of Qt, it does not bring in everything. In particular, if you want to use widgets, you'll need Qt*::Widgets as well.
A good way to ensure you have everything you need is to look at the documentation for the classes you wish to use. For example, the QWidget documentation page (for Qt5, which is what I use) has this in the table at the top:
+-----------+--------------------+
| Header: | #include <QWidget> |
+-----------+--------------------+
| qmake: | QT += widgets |
+-----------+--------------------+
That means you need to include the QWidget header file and link with the widgets library. Were you using qmake, that would simply involve putting that exact line QT += widgets into your project file.
The equivalent in cmake would result in the following changes to your CMakeLists.txt file:
target_link_libraries(VentanaPrincipal
Qt${QT_VERSION_MAJOR}::Core
Qt${QT_VERSION_MAJOR}::Widgets
)
The equivalent Qt6 documentation page is even better since it now shows the cmake stuff as well, meaning you don't need to think about translating the qmake variant:
+-----------+------------------------------------------------------+
| Header: | #include <QWidget> |
+-----------+------------------------------------------------------+
| CMake: | find_package(Qt6 COMPONENTS Widgets REQUIRED) |
| | target_link_libraries(mytarget PRIVATE Qt6::Widgets) |
+-----------+------------------------------------------------------+
| qmake: | QT += widgets |
+-----------+------------------------------------------------------+

Answer 2

How about using QApplicacion instead of QCoreApplication?
QApplication a(argc, argv);
You also don't need cmake. You should create simple project, and use qmake to generate makefile.
Chcek this thread: Simple Qt program builds but doesn't show output.