QGIS 3 C++ API, QgsApplication crash

Question

I'm trying to create a simple application using QGIS 3 SDK. I have used osgeo4w-setup-x86_64.exe for installing QGIS, and I have also installed qgis-dev and qgis-ltr-dev and Qt5. I have set up my .pro file like this:

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++11

INCLUDEPATH += "C:\OSGeo4W64\apps\qgis-ltr-dev\include" \
                "C:\OSGeo4W64\apps\qgis-ltr-dev\bin"

LIBS += -L"C:\OSGeo4W64\apps\qgis-ltr-dev\lib" -lqgis_core -lqgis_gui -lqgis_app

SOURCES += \
    main.cpp 

and the main.cpp is like this:

#include <qgsapplication.h>

#include <QDebug>
int main(int argc, char *argv[])
{
    qDebug() << "*** QGS Application Instance Created *** ";

    QgsApplication app(argc, argv, true);
    int exitCode= app.exec();

    return exitCode;
}

I run my code in this enviroment:

Windows 10 
Qt 5.15.1(MSVC 2019) 
Qt Creator 4.13.1  
QGIS 3.x.x

This code is compiled correctly. But, the problem is when I run it, the program crash even before entering the main function. When I comment the line QgsApplication app(argc, argv, true);, the crash does not happen. I believe there is some problem with linking the QGIS to my application.

How can I fix this?

Have I done something wrong?

Haven't I considered something in setting up the environment?

Answer 1

I have found the answer in here. But a new problem is raised.

I put a breakpoint on the line QgsApplication app(argc, argv, true) and the debugger pops up this:

And at the end of the program, when the line return app.exec(); run, this warning is displayed on the console.

QApplication::exec: Please instantiate the QApplication object first

PS: I explain the problem completely here.