Dear fellow Qt progammers,

I am rather new to C++/Qt and programming in general (although I have quite abit bit of experience in scripting languages as bash, Matlab etc.)

As a start, I am writing a program that does conversions between units (e.g. length (km to miles), area (sq m to sq ft) etc.)

1. I have created a small widget that has four fields:
- inputLine (QLineEdit) : input value field
- sourceUnit (QComboBox) : input unit

- resultLine (QLineEdit) : target value field
- targetUnit (QComboBox) : target unit

The goal is that the end user selects input & target unit, and the input value is converted to the target as it is typed (I used a QDoubleValidator to check for a double, and a simple SIGNAL/SLOT to make appear the input immedately in the target value field (without conversion)). At the moment, the units are only placeholders. This worked fine.

Qt Code: 
  1. #ifndef DCONVERT_H
  2. #define DCONVERT_H
  3.  
  4. #include <QWidget>
  5.  
  6. class QLineEdit;
  7. class QComboBox;
  8.  
  9. class Dconvert : public QWidget
  10. {
  11.     Q_OBJECT
  12.  
  13.     public:
  14.         Dconvert();
  15.  
  16.     public slots:
  17.         void convert();
  18.  
  19.     private:
  20.         QLineEdit *inputLine;
  21.         QLineEdit *resultLine;
  22.         QComboBox *sourceUnit;
  23.         QComboBox *targetUnit;
  24.     };
  25. #endif // DCONVERT_H
  26.  
  27.  
  28. #include <QtGui>
  29. #include "dconvert.h"
  30.  
  31. Dconvert::Dconvert()
  32. {
  33.     QGroupBox *sourceBox = new QGroupBox(tr("From..."));
  34.     QLabel *sourceVal = new QLabel(tr("Value:"));
  35.     inputLine = new QLineEdit;
  36.     sourceUnit = new QComboBox;
  37.  
  38.     sourceUnit->addItem(tr("km"));
  39.     sourceUnit->addItem(tr("Nautical mile"));
  40.  
  41.     QGroupBox *targetBox = new QGroupBox(tr("To..."));
  42.     QLabel *targetVal = new QLabel(tr("Value:"));
  43.     resultLine = new QLineEdit;
  44.     targetUnit = new QComboBox;
  45.  
  46.     targetUnit->addItem(tr("km"));
  47.     targetUnit->addItem(tr("Nautical mile"));
  48.  
  49.     QPushButton *quitButton = new QPushButton(tr("Quit"));
  50.  
  51.     connect(inputLine,SIGNAL(textChanged(QString)),this,SLOT(convert()));
  52.  
  53.     QHBoxLayout *inputLayout = new QHBoxLayout;
  54.     inputLayout->addWidget(sourceVal);
  55.     inputLayout->addWidget(inputLine);
  56.     inputLayout->addWidget(sourceUnit);
  57.  
  58.     QHBoxLayout *targetLayout = new QHBoxLayout;
  59.     targetLayout->addWidget(targetVal);
  60.     targetLayout->addWidget(resultLine);
  61.     targetLayout->addWidget(targetUnit);
  62.  
  63.     QVBoxLayout *mainLayout = new QVBoxLayout;
  64.     mainLayout->addLayout(inputLayout);
  65.     mainLayout->addLayout(targetLayout);
  66.  
  67.  
  68.     setLayout(mainLayout);
  69.  
  70.  
  71.     setWindowTitle(tr("DConvert!"));
  72.  
  73.  
  74.         }
  75. void Dconvert::convert()
  76. {
  77.     resultLine->setText(inputLine->text());
  78. }
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Next, I want the input string from inputLine to be regarded as a double, to be processed and returned to the resultLine.

Now, here the problems begin:

From QString to double seems to work, but after processing it doesnt.... This must be a very basic problem but I just don't find the solution... help please!

Qt Code: 
  1. ...
  2. connect(inputLine,SIGNAL(textChanged(QString)),this,SLOT(convert()));
  3. ...
  4. ...
  5. void Dconvert::convert()
  6. {
  7.  
  8.     double *resultaat = new double;
  9.     resultaat = (double*) &inputLine->text();
  10.     resultLine->setText(QString (*resultaat));
  11. }
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After compiling, this is the error I receive:

Qt Code: 
  1. dconvert.cpp:58: error: conversion from `double' to `QChar' is ambiguous
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