How to use explicit labels/ticks?

Hi, I have very newbie-style problem.
I've written this code:

Code:

---

#include "qwt_plot.h"
#include "qwt_scale_div.h"
#include <QApplication>
 
int main(int argc, char ** argv) {
  QApplication app(argc, argv);
 
  QwtPlot plot;
  plot.setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
  plot.setCanvasBackground(Qt::white);
  plot.setAxisScale(QwtPlot::yLeft, 0, 50);
 
  QList<double> ticks = QList<double>()
   << 10
   << 40
   << 90;
  QwtScaleDiv pressScaleDiv;
  pressScaleDiv.setTicks(QwtScaleDiv::MajorTick, ticks);
  plot.setAxisScaleDiv(QwtPlot::yLeft, pressScaleDiv);
 
  plot.show();
  return app.exec();
 
}

---

My wish is, that y axis has ticks and labels at values 10, 40, 90.
It seems like code above gives no effect - labels are at 0, 10, 20, 30, 40, 50 + intermediate ticks.
What am I doing wrong?
I suspect that the error is trivial :o ....

A QwtScaleDiv consists of the range of a scale and the positions of its ticks. Your code creates an invalid QwtScaleDiv object for 2 reasons:

1. it doesn't have a range
2. QwtScaleDiv::isValid() is only true, when using the constructor with a valid range

The second reason is left over from the very early Qwt versions - it should have never been like this. That's why the isValid() flag has been removed in Qwt 6.1.

Uwe

PS: The line with setAxisScale() is pointless, when you assign a different scale a couple of lines below

Thanks, Uwe.
I've improved my wonderful code:

Code:

---

#include "qwt_plot.h"
#include "qwt_scale_div.h"
#include <QApplication>
 
int main(int argc, char ** argv) {
  QApplication app(argc, argv);
 
  QwtPlot plot;
  plot.setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
  plot.setCanvasBackground(Qt::white);
 
 
  QList<double> ticks[QwtScaleDiv::NTickTypes] = {
    QList<double>(),
    QList<double>(),
    QList<double>()
    << 10
    << 40
    << 90
  };
  QwtScaleDiv pressScaleDiv(0, 100, ticks);
 
  // QwtScaleDiv pressScaleDiv;
  // pressScaleDiv.setInterval(0, 100);
  // pressScaleDiv.setTicks(
  //   QwtScaleDiv::MinorMajor,
  //   QList<double>()
  //   << 10
  //   << 40
  //   << 90
  //   );
  plot.setAxisScaleDiv(QwtPlot::yLeft, pressScaleDiv);
 
  plot.show();
  return app.exec();
 
}

---

and it works - but when I use the commented section instead of the working one above - it doesn't. No problem for me, anyway.
Thanks a lot.

Quote:

---

Originally Posted by ssample

but when I use the commented section instead of the working one above - it doesn't.

---

That's because of what I wrote as 2.). The code would be o.k. for Qwt 6.1, but all earlier versions ( starting with Qwt 0.1 ) have this nasty QwtScaleDiv default constructor.

Uwe