undefined reference to `QwtPlot::qt_metacall(QMetaObject::Call, int, void**)'

I'm struggling to get a QWT plot into my application with so little documentation -- an official intro/howto guide would be helpful. The few examples lingering around the net are from different versions that use very different syntax, etc....

Ok, /rant.

I'm trying to compile this as a generic plot of y = x^2 for the moment:
histPlot.cpp:

Code:

---

#include <qwt5/qwt_plot.h>
#include <qwt5/qwt_plot_curve.h>
#include "histPlot.h"
#include <QWidget>
 
HistPlot::HistPlot( QWidget *parent ) : QwtPlot( parent)
{
  // Show a title
  setTitle( "History" );
 
  // Create curves
  QwtPlotCurve * curve = new QwtPlotCurve("Curve");
 
  double x[100], y[100];
 
  for (int i = 0; i < 100; i++){
    x[i] = i;
    y[i] = i*i;
  }
 
  curve->setData(x,y,100);
  curve->attach(this);
 
  // Show the plots
  replot();
 
}

---

But I get this from the compiler:

Quote:

---

g++ -o timeClock dialogs.o fileOps.o frame.o histPlot.o main.o mainWindow.o timeFunctions.o timeSheet.o moc_frame.o moc_histPlot.o moc_mainWindow.o -L/usr/lib64/qt4 -lqwt -lQtGui -L/usr/lib64 -L/usr/lib64/qt4 -L/usr/X11R6/lib64 -lpng -lSM -lICE -lXi -lXrender -lXrandr -lXinerama -lfreetype -lfontconfig -lXext -lX11 -lQtCore -lz -lm -lrt -ldl -lpthread
moc_histPlot.o: In function `HistPlot::qt_metacall(QMetaObject::Call, int, void**)':
moc_histPlot.cpp:(.text+0x11): undefined reference to `QwtPlot::qt_metacall(QMetaObject::Call, int, void**)'
moc_histPlot.o: In function `HistPlot::qt_metacast(char const*)':
moc_histPlot.cpp:(.text+0x58): undefined reference to `QwtPlot::qt_metacast(char const*)'
moc_histPlot.o:(.rodata+0x0): undefined reference to `QwtPlot::staticMetaObject'
collect2: ld returned 1 exit status
make: *** [timeClock] Error 1

---

Neither I nor google have any idea what qt_metacall is, nor why it can't be found. Any ideas?

The ever-friendly folks in #qt have pointed out that these errors usually result from not moc'ing a header with a Q_OBJECT call. the header for histPlot.cpp does indeed call Q_OBJECT, but it also does get moc'ed. Upon hearing this, #qt told me to find #qwt :) Since #qwt does not exist, I suppose this is the next best thing. Any ideas?

Maybe the linker has problems in finding Qwt? Do you have libqwt.so file on your system?

The qwt library is in my linking path, but it does seem to be a problem with the linker.

Removing Q_OBJECT macro from the histPlot.h header didn't help. Let me know if theres anything else that would be helpful to see -- I'd really like to resolve this quickly :)

The error changes a bit when Q_OBJECT is removed:

Code:

---

histPlot.o:(.rodata._ZTV8HistPlot[vtable for HistPlot]+0x18): undefined reference to `QwtPlot::qt_metacast(char const*)'
histPlot.o:(.rodata._ZTV8HistPlot[vtable for HistPlot]+0x20): undefined reference to `QwtPlot::qt_metacall(QMetaObject::Call, int, void**)'
collect2: ld returned 1 exit status
make: *** [timeClock] Error 1

---

Got it working. Updated to the latest Qwt and linking completes.

I have the same problem, only I'm already using qwt-5.2.0 so I can't update.
This project works on another computer not mine. I can compile and run qwt examples
Any ideas what the problem might be?

I don't have a build environment handy to verify this advice, but the error looks familiar...

Make sure QWT_DLL is defined in your compiler flags.

I solved this problem by changing the install dir of qwt to /usr, this in linux

Quote:

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Originally Posted by mendes

I solved this problem by changing the install dir of qwt to /usr, this in linux

---

Whatever solved the problem in your particular situation - changing the install dir to /usr has absolutely nothing to do with it.

Uwe

I receive the same error when I changed qwt from shared lib to static library under linux. any idea what may be the issue? thanks.