Subclassing QDoubleSpinBox with NaN value - c++

Question

I subclassed QDoubleSpinBox in order to make a QDoubleSpinBox that allows the user to enter NaN as valid input. Right now if a user enters "nan" into the spinbox the control is automatically changing the text to the value of DBL_MAX instead of staying as nan. Before i started using the math.h library with the nan and isnan functions i just defined NAN_VALUE to be 1000 and the range to be -1000 to 1000. Then in my textFromValue i checked if value was equal to NAN_VALUE. Likewise in the valueFromText function i was returning NAN_VALUE. When i did it that way it worked but i would like to be able to use the nan and isnan functions instead. Now that i added in the nan and isnan function calls it stopped working. Does anyone know why that is? Also, i noticed i had this problem with my earlier implementation when i used DBL_MIN and DBL_MAX as the range. Are those numbers too big of a range for the control? If i made the range smaller like -1000 and 1000 it worked fine..
Here is my implementation:
CustomDoubleSpinBox.h
#ifndef CUSTOMDOUBLESPINBOX_H
#define CUSTOMDOUBLESPINBOX_H
#include <QDoubleSpinBox>
#include <QWidget>
#include <QtGui>
#include <iostream>
#include <math.h>
#include <float.h>
#include <limits>
#define NUMBER_OF_DECIMALS 2
using namespace std;
class CustomDoubleSpinBox : public QDoubleSpinBox
{
Q_OBJECT
public:
CustomDoubleSpinBox(QWidget *parent = 0);
virtual ~CustomDoubleSpinBox() throw() {}
double valueFromText(const QString &text) const;
QString textFromValue(double value) const;
QValidator::State validate ( QString & input, int & pos ) const;
};
#endif // CUSTOMDOUBLESPINBOX_H
CustomDoubleSpinBox.cpp
#include "CustomDoubleSpinBox.h"
CustomDoubleSpinBox::CustomDoubleSpinBox(QWidget *parent) : QDoubleSpinBox(parent)
{
this->setRange(DBL_MIN, DBL_MAX);
this->setDecimals(NUMBER_OF_DECIMALS);
}
QString CustomDoubleSpinBox::textFromValue(double value) const
{
if (isnan(value))
{
return QString::fromStdString("NaN");
}
else
{
QString result;
return result.setNum(value,'f', NUMBER_OF_DECIMALS);
}
}
double CustomDoubleSpinBox::valueFromText(const QString &text) const
{
if (text.toLower() == QString::fromStdString("nan"))
{
return nan("");
}
else
{
return text.toDouble();
}
}
QValidator::State CustomDoubleSpinBox::validate ( QString & input, int & pos ) const
{
Q_UNUSED(input);
Q_UNUSED(pos);
return QValidator::Acceptable;
}