How to link with Qt?

[Csáti Zoltán]

Dear all,

I ran a QMathGL example from here: http://mathgl.sourceforge.net/doc_en/Using-QMathGL.html:

#include <QApplication>
#include <QMainWindow>
#include <QScrollArea>
#include <mgl2/qmathgl.h>

int sample(mglGraph *gr);

int main(int argc,char **argv)
{
  QApplication a(argc,argv);
  QMainWindow *Wnd = new QMainWindow;
  Wnd->resize(810,610);  // for fill up the QMGL, menu and toolbars
  Wnd->setWindowTitle("QMathGL sample");
  // here I allow to scroll QMathGL -- the case
  // then user want to prepare huge picture
  QScrollArea *scroll = new QScrollArea(Wnd);
  // Create and setup QMathGL
  QMathGL *QMGL = new QMathGL(Wnd);
  // QMGL->setPopup(popup); // if you want to setup popup menu for QMGL
  QMGL->setDraw(sample);
  // or use QMGL->setDraw(foo); for instance of class Foo:public mglDraw
  QMGL->update();

  // continue other setup (menu, toolbar and so on)
  scroll->setWidget(QMGL);
  Wnd->setCentralWidget(scroll);
  Wnd->show();
  return a.exec();
}

int sample(mglGraph *gr)
{
    gr->SubPlot(1, 1, 0, "");
    gr->Box();
    gr->Axis();
    gr->Grid("xy", ";k");
    gr->FPlot("sin(pi*x)", "2r");
    return 1;
}

 I couldn't link it from QtCreator, so I did it from the Terminal:

g++ -m64 -pipe -g -Wall -W -D_REENTRANT -fPIE -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I/usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++-64 -I../MathGL -I/usr/include/qt5 -I/usr/include/qt5/QtWidgets -I/usr/include/qt5/QtGui -I/usr/include/qt5/QtCore -I. -I. -I. -lmgl-qt5 -lmgl -std=gnu++11 main.cpp

which gave the error:

/tmp/ccSxmbTR.o: In function `main':
/home/zoli/MathGL/main.cpp:12: undefined reference to `QApplication::QApplication(int&, char**, int)'
/home/zoli/MathGL/main.cpp:13: undefined reference to `QMainWindow::QMainWindow(QWidget*, QFlags<Qt::WindowType>)'
/home/zoli/MathGL/main.cpp:15: undefined reference to `QWidget::setWindowTitle(QString const&)'
/home/zoli/MathGL/main.cpp:18: undefined reference to `QScrollArea::QScrollArea(QWidget*)'
/home/zoli/MathGL/main.cpp:20: undefined reference to `QMathGL::QMathGL(QWidget*, QFlags<Qt::WindowType>)'
/home/zoli/MathGL/main.cpp:24: undefined reference to `QMathGL::update()'
/home/zoli/MathGL/main.cpp:27: undefined reference to `QScrollArea::setWidget(QWidget*)'
/home/zoli/MathGL/main.cpp:28: undefined reference to `QMainWindow::setCentralWidget(QWidget*)'
/home/zoli/MathGL/main.cpp:29: undefined reference to `QWidget::show()'
/home/zoli/MathGL/main.cpp:30: undefined reference to `QApplication::exec()'
/home/zoli/MathGL/main.cpp:30: undefined reference to `QApplication::~QApplication()'
/home/zoli/MathGL/main.cpp:30: undefined reference to `QApplication::~QApplication()'
/tmp/ccSxmbTR.o: In function `QString::QString(char const*)':
/usr/include/qt5/QtCore/qstring.h:579: undefined reference to `QString::fromAscii_helper(char const*, int)'
/tmp/ccSxmbTR.o: In function `QWidget::resize(int, int)':
/usr/include/qt5/QtWidgets/qwidget.h:830: undefined reference to `QWidget::resize(QSize const&)'
/tmp/ccSxmbTR.o: In function `mglGraph::SubPlot(int, int, int, char const*, double, double)':
/usr/local/include/mgl2/mgl.h:286: undefined reference to `mgl_subplot_d'
/tmp/ccSxmbTR.o: In function `mglGraph::Box(char const*, bool)':
/usr/local/include/mgl2/mgl.h:703: undefined reference to `mgl_box_str'
/tmp/ccSxmbTR.o: In function `mglGraph::Axis(char const*, char const*, char const*)':
/usr/local/include/mgl2/mgl.h:722: undefined reference to `mgl_axis'
/tmp/ccSxmbTR.o: In function `mglGraph::Grid(char const*, char const*, char const*)':
/usr/local/include/mgl2/mgl.h:725: undefined reference to `mgl_axis_grid'
/tmp/ccSxmbTR.o: In function `mglGraph::FPlot(char const*, char const*, char const*)':
/usr/local/include/mgl2/mgl.h:1894: undefined reference to `mgl_fplot'
/tmp/ccSxmbTR.o: In function `QMathGL::setDraw(int (*)(mglGraph*))':
/usr/local/include/mgl2/qmathgl.h:61: undefined reference to `mgl_draw_graph'
/usr/local/include/mgl2/qmathgl.h:61: undefined reference to `QMathGL::setDraw(int (*)(mglBase*, void*), void*)'
/tmp/ccSxmbTR.o: In function `QTypedArrayData<unsigned short>::deallocate(QArrayData*)':
/usr/include/qt5/QtCore/qarraydata.h:230: undefined reference to `QArrayData::deallocate(QArrayData*, unsigned long, unsigned long)'
collect2: error: ld returned 1 exit status

Why is the error? The problem is connected to Qt, as a simple MathGL example compiled without problems.

Thank you,
Zoltan

[Csáti Zoltán]

I realized that the linking libraries must follow the executable and not precede it:

g++ -m64 -pipe -g -Wall -W -D_REENTRANT -fPIE -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I/usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++-64 -I../MathGL -I/usr/include/qt5 -I/usr/include/qt5/QtWidgets -I/usr/include/qt5/QtGui -I/usr/include/qt5/QtCore -I. -I. -I. -std=gnu++11 main.cpp -lmgl -lmgl-qt5

Now, the error reduced to

/usr/bin/ld: /tmp/cc8J2ZMS.o: undefined reference to symbol '_ZN7QString16fromAscii_helperEPKci'
//usr/lib/x86_64-linux-gnu/libQt5Core.so.5: error adding symbols: DSO missing from command line