QGIS Standalone C++ Application with Qt: "The program has unexpectedly finished"

Question

I'm trying to develop an Standalone Application with Qt and QGIS API.

There are several code examples that should work, but they don't.

The Problem is that everytime I use "QgsApplication" the application Output says: "The program has unexpectedly finished."

Even this simple code does not work:

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

#include "qgsapplication.h"

int main(int argc, char *argv[])
{
    QgsApplication app(argc, argv, true);
}  

My Project.pro file:

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = Project
TEMPLATE = app


SOURCES += main.cpp\
    mainwindow.cpp

HEADERS  += mainwindow.h

FORMS    += mainwindow.ui

LIBS += -L"C:/QGIS Building/lib" -lqgis_core -lqgis_gui

INCLUDEPATH += "C:/QGIS Building/include"

DEFINES +=      CORE_EXPORT=""
DEFINES +=      GUI_EXPORT=""

Answer 1

I had similar problems, when I try to run a standalone QGis App. Important is that you call QApplication at first and then set context path for QGIS with

   QgsApplication::setPrefixPath("/usr", true);

(in LINUX) before you call.

   QgsApplication::initQgis();

A program initialisation that works for me looks like this.

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

 int main(int argc, char *argv[]) {

   // 1. Initialize App
   QApplication app(argc, argv);
   QgsApplication::setPrefixPath("/usr", true);
   QgsApplication::initQgis();

    //2. App start
    MainWindow win(config, db);
    win.show();
    int result = app.exec();

    //3. Qgis free libs
    QgsApplication::exitQgis();

    //4. And say goodby
    return result;
 }