[Solved] Mathematical Operations on Input Strings. A short way?
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Hi all,
I have an input text edit box and an output text edit box. The latters output is double the value of the input. IN order for me to do this, I executed 4 lines of code as follows:
@ QString inputstring = ui -> A1 ->text();
double inputstring_d = inputstring.toDouble();
QString outputstring = QString::number (2*inputstring_d);
ui->slot_capacity_required->setText(outputstring);@It works just fine but its tedious work converting a QString to a double, doing a mathematical operation on it, then converting back to QString on output. Surely there must be a shortcut?
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If you don't want to do all the QString conversion you should replace de QTextEdit with a "QDoubleSpinBox":http://qt-project.org/doc/qt-5.0/qtwidgets/qdoublespinbox.html
For example:
@ // pointers to ui objects
QDoubleSpinBox spinBox_1 = new QDoubleSpinBox(this);
QDoubleSpinBox spinBox_2 = new QDoubleSpinBox(this);
// multiplication and value setting
spinBox_2->setValue(2*spinBox_1->value());@If you don't want the arrows just do the following:
@spinBox_1->setButtonSymbols(QAbstractSpinBox::NoButtons);@ -
Ah, okay the double spin box works better as it deals with numbers and not strings, thanks.
However, I had to drag the boxes in the user interface as the statements QDoubleSpinBox spinBox_1 = new QDoubleSpinBox(this);
QDoubleSpinBox spinBox_2 = new QDoubleSpinBox(this);
give and error: conversion from 'QDoubleSpinBox*' to non-scalar type 'QDoubleSpinBox' requested -
There's a typo in Seba's code
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Is there any way I can remove trailing zero's in the user input?
Say I want 5 decimal places for accuracy and the user inputs 0.05, the widget will automatically show 0.0500.
I searched for answers and someone mentions:
You can subclass the QDoubleSpinBox class and reimplement textFromValue() and format the number any way you want it.and an other person:
Subclass and reimplement textFromValue().How do I do that exactly?
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Doesn't this do the job?
@ spinBox->setDecimals(5); @EDIT: Sorry I now understand the problem, I have answered too fast! :)
This should do the work:
@
#include <QDoubleSpinBox>class mySpinBox: public QDoubleSpinBox {
mySpinBox(QObject *_parent =0) : QDoubleSpinBox(_parent) { setDecimals(5); }
QString textFromValue(double value) const {
QString str = QWidget::locale().toString(value, QLatin1Char('f'), decimals());
for(int i = str.size()-1; str[i]=='0'; i--) {
str.remove(i,1);
}
}
};
@Code not tested.
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Then I would recommend grabbing a good C++ book before going further. These two concepts are basics that you need to know. On a side note many examples in Qt's documentation uses both.
Subclassing: creating a class that inherits from another one e.g. QWidget is a QObject
Reimplementing: valid only for virtual methods, rewrite a method to do things differently from the original or do additional operations before/after calling the original implementation.
