QwtPlot build error (undefined reference...)

[yeshe66]

Hi

I am new to Qt and even more new to Qwt.

It is the first time I am using Qwt, and I can't compile it.

I am using QT Creator 2.1.80 (based on Qt 4.7.0) and have made a "MainWindow" in the graphic "Form" editor.

Screenshot:
http://s3.postimage.org/2d7ctc9tw/Qwt_Plot.jpg (http://postimage.org/image/2d7ctc9tw/)

When I try to compile this , the error occurs in ui_mainwindow.h: 107: error: undefined reference to `QwtPlot::QwtPlot(QWidget*)'

line 107:

centralWidget = new QWidget(MainWindow);
centralWidget->setObjectName(QString::fromUtf8("centralWidget"));
qwtKurva = new QwtPlot(centralWidget); // **** LINE 107 ****
qwtKurva->setObjectName(QString::fromUtf8("qwtKurva"));
qwtKurva->setEnabled(false);
qwtKurva->setGeometry(QRect(10, 40, 521, 211));

The code is generated automatically, so I don't know what is causing the problem.