Using QGIS C++ API In Custom GIS Application

Question

I'm trying to develop a custom GIS application using Qt. Which will show a map and have some figure drawing options on the map. While searching on the web, I came across with QGIS. I wonder if I could use QGIS C++ API (QgsMapCanvas etc.) for basic map functionality in my app.

I wrote a simple Qt Application to use QGIS API. It is compiled and linked successfully. But when I tried to run the application it gives: " The program has unexpectedly finished." error. And crashes.

My development environment:

• Qt 5.12.0
• MSVC 2015
• Windows 10 x64
• OSGeo4W64 is installed including "qgis-ltr-dev" package (QGIS version 3.11.0-8) http://download.osgeo.org/osgeo4w/osgeo4w-setup-x86_64-v1.exe (64bit) (link updated - 2018-Feb-26)

My pro file:

#-------------------------------------------------
#
# Project created by QtCreator 2020-06-10T09:28:31
#
#-------------------------------------------------

QT       += core gui xml

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = Hello_QGis_2
TEMPLATE = app

CONFIG += c++11

SOURCES += main.cpp

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

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

DEFINES+=CORE_EXPORT=
DEFINES+=GUI_EXPORT=

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

Source Code (main.cpp):

#include <QApplication>

#include <qgsapplication.h>
#include <QtDebug>

int main(int argc, char *argv[])
{
    QgsApplication app(argc, argv, true);
    qDebug() << "*** QGS Application Instance Created *** ";

    qDebug() << "*** setPrefixPath to C:\\OSGeo4W64\\apps\\qgis-ltr-dev *** ";
    QString PREFIX_PATH = "C:\\OSGeo4W64\\apps\\qgis-ltr-dev";

    QgsApplication::setPrefixPath(PREFIX_PATH);

    qDebug() << "*** initQgis ***";
    QgsApplication::initQgis();

    int exitCode= app.exec();

    QgsApplication::exitQgis();

    qDebug() << "*** Finished *** ";

    return exitCode;
}

I also used following bat file to start Qt Creator: (As mentioned in QT C++ application using QGIS API)

ECHO Setting up QGIS DEV ENV

set PYTHONPATH=

set OSGEO4W_ROOT=C:\OSGeo4W64
call "%OSGEO4W_ROOT%\bin\o4w_env.bat"

@set QMAKESPEC=win64-msvc2015

@set PATH=%OSGEO4W_ROOT%\bin;%OSGEO4W_ROOT%\apps\qgis-ltr-dev\bin;%PATH%

@set INCLUDE=%INCLUDE%;%OSGEO4W_ROOT%\include;%OSGEO4W_ROOT%\apps\qgis-ltr-dev\include

@set LIB=%LIB%;%OSGEO4W_ROOT%\lib;%OSGEO4W_ROOT%\apps\qgis-ltr-dev\lib

path %OSGEO4W_ROOT%\bin;%SYSTEMROOT%\System32;%SYSTEMROOT%;%SYSTEMROOT%\System32\wbem;C:\OSGeo4W64\apps\Qt5\bin;C:\OSGeo4W64\apps\Qt5\Tools\QtCreator\bin;%PATH%

set VS140COMNTOOLS=C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\Tools
call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x64

start "Qt Creator" /B D:\Development\Qt\Qt5.12.0\Tools\QtCreator\bin\qtcreator.exe %*

As I read from the documentation, the library files for Windows (*.dll) in OsGeo4W64 produced using MSVC 2015. And I tried to use those libraries with the same compiler. So I can not figure out what am I missing?

Answer 1

The problem is solved. I think the problem was about setting the required environment variables by QGIS.

I used the following bat file when launching Qt Creator. This fixed my problem.

PATH=C:\OSGEO4~1\apps\qgis-ltr-dev\bin;C:\OSGEO4~1\apps\gdal-dev\pymod3\scripts;C:\OSGEO4~1\apps\Python37;C:\OSGEO4~1\apps\Python37\Scripts;C:\OSGEO4~1\apps\gdal-dev\bin;C:\OSGEO4~1\apps\proj-dev\bin;C:\OSGEO4~1\apps\qt5\bin;C:\OSGEO4~1\bin;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\system32\WBem;%PATH%
set GDAL_DATA=C:\OSGEO4~1\apps\gdal-dev\share\gdal
set GDAL_DRIVER_PATH=C:\OSGEO4~1\apps\gdal-dev\bin\gdalplugins
set GDAL_FILENAME_IS_UTF8=YES
set GEOTIFF_CSV=C:\OSGEO4~1\share\epsg_csv
set JPEGMEM=1000000
set OSGEO4W_ROOT=C:\OSGEO4~1
set PROJ_LIB=C:\OSGEO4~1\apps\proj-dev\share\proj
set PYTHONHOME=C:\OSGEO4~1\apps\Python37
set PYTHONPATH=C:\OSGEO4~1\apps\gdal-dev\pymod3\lib\site-packages;C:\OSGEO4~1\apps\Python37;C:\OSGEO4~1\apps\Python37\Scripts
set QGIS_PREFIX_PATH=C:/OSGEO4~1/apps/qgis-ltr-dev
set QT_PLUGIN_PATH=C:\OSGEO4~1\apps\qgis-ltr-dev\qtplugins;C:\OSGEO4~1\apps\qt5\plugins
set VSI_CACHE=TRUE
set VSI_CACHE_SIZE=1000000
set O4W_QT_PREFIX=C:/OSGEO4~1/apps/Qt5
set O4W_QT_BINARIES=C:/OSGEO4~1/apps/Qt5/bin
set O4W_QT_PLUGINS=C:/OSGEO4~1/apps/Qt5/plugins
set O4W_QT_LIBRARIES=C:/OSGEO4~1/apps/Qt5/lib
set O4W_QT_TRANSLATIONS=C:/OSGEO4~1/apps/Qt5/translations
set O4W_QT_HEADERS=C:/OSGEO4~1/apps/Qt5/include

start "Qt Creator" /B  D:\Development\Qt\Qt5.12.0\Tools\QtCreator\bin\qtcreator.exe %*