Qt and QGis integration ERROR `__imp__ZN14QgsApplicationC1ERiPPcbRK7QStringS5_'

[Christian Ehrlicher]

You can not mix MSVC and MinGW c++ libraries - if you want to use MinGW/g++ then you also have to compile OSGeo with MinGW which I doubt you have.

[Aman55]

Can you guide to compile OSGeo with MinGW? @Christian-Ehrlicher . As in OSGeo installer i don't get option to choose MinGw or MSVC.

[jsulm]

@Aman55 said in Qt and QGis integration ERROR `__imp__ZN14QgsApplicationC1ERiPPcbRK7QStringS5_':

Can you guide to compile OSGeo with MinGW?

Please refer to their documentation: https://github.com/qgis/QGIS/blob/master/INSTALL.md

[Aman55]

I have downloaded visual studio 2017 and I updated my compiler with Qt Compiler MSVC 2017. got an error
C:\OSGeo4W\apps\qgis-ltr-dev\include\qgssettingsentry.h:31: error: C7525: inline variables require at least '/std:c++17' @Christian-Ehrlicher @jsulm

[Aman55]

update c++11 to c++17 and build successfully . but 13:39:44: The program has unexpectedly finished. when i run in debug mode it giving ![alt

[jsulm]

@Aman55 Do you have the debug versions of the QGIS libs?

[Aman55]

@jsulm can't say yes. if it comes with download only.

[jsulm]

@Aman55 said in Qt and QGis integration ERROR `__imp__ZN14QgsApplicationC1ERiPPcbRK7QStringS5_':

can't say yes. if it comes with download only.

You can simply check what DLLs where installed.
Does release build work?

[Aman55]

@jsulm Yes release build work for the above main.cpp code. currently used to load shp file and gives error
C:\OSGeo4W\apps\qgis-ltr-dev\include\qgsabstractgeometry.h:596: error: C2065: 'M_PI': undeclared identifier
C:\OSGeo4W\apps\qgis-ltr-dev\include\qgsvector.h:175: error: C2065: 'M_PI': undeclared identifier
C:\OSGeo4W\apps\qgis-ltr-dev\include\qgsgeometry.h:2757: error: C2065: 'M_PI': undeclared identifier

// main.cpp
int main(int argc, char *argv[]) {
    QApplication a(argc, argv);
    // 1. Initialize QGIS
    QgsApplication::setPrefixPath("C:/OSGeo4W64/apps/qgis-ltr-dev", true); // Replace with your QGIS installation path
    QgsApplication::init();

    // 2. Specify the path to your SHP file
    QString shpFilePath = ":/gis_osm_barriers_07_1.shp"; // Replace with the actual path

    // 3. Check if the file exists
    QFileInfo fileInfo(shpFilePath);
    if (!fileInfo.exists()) {
        qDebug() << "Error: Shapefile not found at" << shpFilePath;
        QgsApplication::exit();
        return 1;
    }


    // 4. Create a QgsVectorLayer
    QgsVectorLayer *vlayer = new QgsVectorLayer(shpFilePath, "shapefile_layer", "ogr"); // "ogr" is the data provider

    // 5. Check if the layer is valid
    if (!vlayer->isValid()) {
        qDebug() << "Error: Could not load shapefile:" << vlayer->error().message();
        delete vlayer;
        QgsApplication::exit();
        return 1;
    }

    // 6.  Accessing Feature Information (Example)
    qDebug() << "Number of features:" << vlayer->featureCount();


    // 7. Clean up
    delete vlayer;  // Important to prevent memory leaks
    QgsApplication::exit();

    return 0;
}

[jsulm]

@Aman55 Then you probably only have the release versions of these libs which can't be mixed with a debug build.

"Yes release build work for the above main.cpp code. currently used to load shp file and gives error" - I don't get it. How can it work if you get compiler errors? What is the very first error?

[Aman55]

@jsulm Previously i have only use qgsapplication header as

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


int main(int argc, char *argv[])
{
  QgsApplication app(argc, argv, true);
  QgsApplication::setPrefixPath("C:/OSGeo4W64/apps/qgis-ltr-dev", true);

  int retval = app.exec();
//  QgsApplication::exitQgis();
  return retval;
}

so there is no need for other headerfiles. then it build successfully. Now i am reading shp file where it does not locate M_PI Macro

[Aman55]

it build successfully but giving some runtime error unable to pinpoint as it only gives The program has unexpectedly finished. After including #include <qgsapplication.h>

[JonB]

@Aman55 So far as I can see you have not tried to show the stack trace from a debugger when it crashes.

[Aman55]

@JonB In debug mode i got error of CDB process terminated

[JonB]

@Aman55 Yes, you need to look at the stack trace pane in the debugger when that happens, so that you know where it comes from.