Showing numbers in decimal not scientific notation
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I simplified the code as follows. This, too, has exactly that problem:
test.h#ifndef TEST_H #define TEST_H #include <QDialog> class QLineEdit; class QPushButton; class test : public QDialog { Q_OBJECT public: test(QWidget* parent = 0); private slots: void expression(); private: QLineEdit* result_box; QPushButton* equal; QPushButton* quit; }; #endif // TEST_Htest.cpp#include <QtWidgets> #include "test.h" test::test(QWidget* parent) : QDialog(parent) { result_box = new QLineEdit; equal = new QPushButton(tr("=")); quit = new QPushButton(tr("Close")); connect(quit, SIGNAL(clicked(bool)), this, SLOT(close())); connect(equal,SIGNAL(clicked(bool)), this, SLOT(expression())); QHBoxLayout* layout = new QHBoxLayout; layout -> addWidget(result_box); layout -> addWidget(equal); layout -> addWidget(quit); setLayout(layout); } //****************** void test::expression() { QString ss; double d = 1000000; QTextStream (&ss) << d; result_box -> setText(ss); }And
main.cpp#include <QApplication> #include "test.h" int main(int argc, char* argv[]) { QApplication app(argc, argv); test t; t.show(); return app.exec(); }Just run it and click on the
=button. -
I think I should write a code for it like this:
if( d is like an int number) result_box -> setText(QString::number(d , 'f', 0)); else if ( d is a double number with n numbers after point) result_box -> setText(QString::number(d , 'f', n)); -
expression() returns an int or double value.
I'm pretty sure that functions returns a string, not an
int, nor adouble.Don't be that sure. :)
I have this method in my code:double My_First_Calculator::expression()But I think this error is of that
ssis aQString.@tomy said in Showing numbers in decimal not scientific notation:
Don't be that sure. :)
Yes! There's a typo in the code ... :)
ss = qFuzzyCompare(expression(), static_cast<qint64>(expression()) ? //< Missing a ) QString::number(static_cast<qint64>(expression())) : QString::number(expression(), 'f')); //< Extra )What you want is to have the
ifwithqFuzzyCompare, not with the static cast. It should rather read like this:ss = qFuzzyCompare(expression(), static_cast<qint64>(expression())) ? QString::number(static_cast<qint64>(expression())) : QString::number(expression(), 'f');If you wish you can of course use the usual
if-elseconstruct, not the ternary operator, so the last snippet'd be equivalent to:if (qFuzzyCompare(expression(), static_cast<qint64>(expression())) ss = QString::number(static_cast<qint64>(expression())); else ss = QString::number(expression(), 'f');Read and abide by the Qt Code of Conduct
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@tomy said in Showing numbers in decimal not scientific notation:
Don't be that sure. :)
Yes! There's a typo in the code ... :)
ss = qFuzzyCompare(expression(), static_cast<qint64>(expression()) ? //< Missing a ) QString::number(static_cast<qint64>(expression())) : QString::number(expression(), 'f')); //< Extra )What you want is to have the
ifwithqFuzzyCompare, not with the static cast. It should rather read like this:ss = qFuzzyCompare(expression(), static_cast<qint64>(expression())) ? QString::number(static_cast<qint64>(expression())) : QString::number(expression(), 'f');If you wish you can of course use the usual
if-elseconstruct, not the ternary operator, so the last snippet'd be equivalent to:if (qFuzzyCompare(expression(), static_cast<qint64>(expression())) ss = QString::number(static_cast<qint64>(expression())); else ss = QString::number(expression(), 'f'); -
@tomy said in Showing numbers in decimal not scientific notation:
Don't be that sure. :)
Yes! There's a typo in the code ... :)
ss = qFuzzyCompare(expression(), static_cast<qint64>(expression()) ? //< Missing a ) QString::number(static_cast<qint64>(expression())) : QString::number(expression(), 'f')); //< Extra )What you want is to have the
ifwithqFuzzyCompare, not with the static cast. It should rather read like this:ss = qFuzzyCompare(expression(), static_cast<qint64>(expression())) ? QString::number(static_cast<qint64>(expression())) : QString::number(expression(), 'f');If you wish you can of course use the usual
if-elseconstruct, not the ternary operator, so the last snippet'd be equivalent to:if (qFuzzyCompare(expression(), static_cast<qint64>(expression())) ss = QString::number(static_cast<qint64>(expression())); else ss = QString::number(expression(), 'f');What you want is to have the
ifwithqFuzzyCompare, not with the static cast. It should rather read like this:ss = qFuzzyCompare(expression(), static_cast<qint64>(expression())) ? QString::number(static_cast<qint64>(expression())) : QString::number(expression(), 'f');If you wish you can of course use the usual
if-elseconstruct, not the ternary operator, so the last snippet'd be equivalent to:if (qFuzzyCompare(expression(), static_cast<qint64>(expression())) ss = QString::number(static_cast<qint64>(expression())); else ss = QString::number(expression(), 'f');Sorry, I don't know how I tested it but it doesn't work as it's expected! :(
for example:
2 + 3 = 5OK
10 ^ 6 = 1000000OK
2 + 1.5 = 3.500000!!!That is, the function
QString::number(expression(), 'f');(with the default precision 6) shows all range of precision whether it's need or not!Maybe it's what we need:
http://doc.qt.io/qt-5/qtextstream.html#setRealNumberNotation
But how to use it? Docs doesn't offer a little example of it to show how beginners should use it. !!!!!!
(Docs are not for learners/beginners, they are for professionals — if they are professional, so they don't need Docs much => Docs are not useful) -
What you want is to have the
ifwithqFuzzyCompare, not with the static cast. It should rather read like this:ss = qFuzzyCompare(expression(), static_cast<qint64>(expression())) ? QString::number(static_cast<qint64>(expression())) : QString::number(expression(), 'f');If you wish you can of course use the usual
if-elseconstruct, not the ternary operator, so the last snippet'd be equivalent to:if (qFuzzyCompare(expression(), static_cast<qint64>(expression())) ss = QString::number(static_cast<qint64>(expression())); else ss = QString::number(expression(), 'f');Sorry, I don't know how I tested it but it doesn't work as it's expected! :(
for example:
2 + 3 = 5OK
10 ^ 6 = 1000000OK
2 + 1.5 = 3.500000!!!That is, the function
QString::number(expression(), 'f');(with the default precision 6) shows all range of precision whether it's need or not!Maybe it's what we need:
http://doc.qt.io/qt-5/qtextstream.html#setRealNumberNotation
But how to use it? Docs doesn't offer a little example of it to show how beginners should use it. !!!!!!
(Docs are not for learners/beginners, they are for professionals — if they are professional, so they don't need Docs much => Docs are not useful)What you want to do in the floating point case is not at all trivial. Here you can read on that topic if you are willing to digest the math.
The simpler but inefficient approach is to save the floating point text representation and just discard all the trailing
0characters manually.EDIT:
Here's (probably) the most concise way, but requires knowledge of regular expressions, which is yet again for you to read on to understand how or why it works:if (qFuzzyCompare(expression(), static_cast<qint64>(expression())) ss = QString::number(static_cast<qint64>(expression())); else { ss = QString::number(expression(), 'f', 17); ss.replace(QRegularExpression("\\.?0+$"), ""); }(Docs are not for learners/beginners, they are for professionals — if they are professional, so they don't need Docs much => Docs are not useful)
You got that backwards. The point of the Qt docs is they are a documentation for Qt itself, they will give no instruction into C++, its types, the types' memory layout and other such technical topics. If you are in need of that, then you need to look elsewhere, for example http://en.cppreference.com/w/
Read and abide by the Qt Code of Conduct
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What you want to do in the floating point case is not at all trivial. Here you can read on that topic if you are willing to digest the math.
The simpler but inefficient approach is to save the floating point text representation and just discard all the trailing
0characters manually.EDIT:
Here's (probably) the most concise way, but requires knowledge of regular expressions, which is yet again for you to read on to understand how or why it works:if (qFuzzyCompare(expression(), static_cast<qint64>(expression())) ss = QString::number(static_cast<qint64>(expression())); else { ss = QString::number(expression(), 'f', 17); ss.replace(QRegularExpression("\\.?0+$"), ""); }(Docs are not for learners/beginners, they are for professionals — if they are professional, so they don't need Docs much => Docs are not useful)
You got that backwards. The point of the Qt docs is they are a documentation for Qt itself, they will give no instruction into C++, its types, the types' memory layout and other such technical topics. If you are in need of that, then you need to look elsewhere, for example http://en.cppreference.com/w/
The point of the Qt docs is they are a documentation for Qt itself, they will give no instruction into C++, its types, the types' memory layout and other such technical topics.
Thanks but I didn't talk about C++, but Docs.
I thought we can look at the Docs as a set of instructions useful for learners to be used to Qt, because they have been frequently suggested to new comers of Qt for reading.
Thanks also for your code. -
The point of the Qt docs is they are a documentation for Qt itself, they will give no instruction into C++, its types, the types' memory layout and other such technical topics.
Thanks but I didn't talk about C++, but Docs.
I thought we can look at the Docs as a set of instructions useful for learners to be used to Qt, because they have been frequently suggested to new comers of Qt for reading.
Thanks also for your code.@tomy Qt documentation is not a set of instructions and it will never be. It is just not possible to have instructions for every use case you can imagine.
Qt documentation documents Qt API and provides some examples. For specific use cases you need to think about it, read Qt documentation, try out. This is same for all frameworks I was using so far. -
The point of the Qt docs is they are a documentation for Qt itself, they will give no instruction into C++, its types, the types' memory layout and other such technical topics.
Thanks but I didn't talk about C++, but Docs.
I thought we can look at the Docs as a set of instructions useful for learners to be used to Qt, because they have been frequently suggested to new comers of Qt for reading.
Thanks also for your code.@tomy said in Showing numbers in decimal not scientific notation:
I thought we can look at the Docs as a set of instructions useful for learners to be used to Qt, because they have been frequently suggested to new comers of Qt for reading.
You can, but the implication is you have a decent knowledge of C++ before that, as Qt is a library that's written and intended to be used from (among others) C++ code. So these are two separate issues you need to address. Learning about Qt without a good fundament is (and always will be) a very, very hard thing to do. Think about it like this, you wouldn't start writing a book in a foreign language, unless you're very intimately familiar with the actual language, right?
Read and abide by the Qt Code of Conduct
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@tomy said in Showing numbers in decimal not scientific notation:
I thought we can look at the Docs as a set of instructions useful for learners to be used to Qt, because they have been frequently suggested to new comers of Qt for reading.
You can, but the implication is you have a decent knowledge of C++ before that, as Qt is a library that's written and intended to be used from (among others) C++ code. So these are two separate issues you need to address. Learning about Qt without a good fundament is (and always will be) a very, very hard thing to do. Think about it like this, you wouldn't start writing a book in a foreign language, unless you're very intimately familiar with the actual language, right?
@kshegunov
First off, I like your attitude. And I wish we all believe in Democracy. Indeed, I use a book for learning Qt. But it's sometimes possible to refer to a good resource for a topic. I know Docs are in a high position in Qt folk's perspectives, but if I can use democracy and say my opinion, I say, "I have not found them useful up to now".
It may change. I've joined Qt just recently.
Thanks for your talks. -
@kshegunov
First off, I like your attitude. And I wish we all believe in Democracy. Indeed, I use a book for learning Qt. But it's sometimes possible to refer to a good resource for a topic. I know Docs are in a high position in Qt folk's perspectives, but if I can use democracy and say my opinion, I say, "I have not found them useful up to now".
It may change. I've joined Qt just recently.
Thanks for your talks. -
Hi,
for your specific situation, I would suggest something like:
QString truncValue(double value, int prec) { QString sReturn = QString::number(value,'f',prec); if(sReturn.endsWith("0")){ while(sReturn.endsWith("0")) sReturn.remove(sReturn.length()-1,1); if(sReturn.endsWith(".")) sReturn.remove(sReturn.length()-1,1); } return sReturn; }But, this is successively chaining a lot of string operations. The previously mentions methods are probably better.
Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct
Q: What's that?
A: It's blue light.
Q: What does it do?
A: It turns blue. -
Hi,
for your specific situation, I would suggest something like:
QString truncValue(double value, int prec) { QString sReturn = QString::number(value,'f',prec); if(sReturn.endsWith("0")){ while(sReturn.endsWith("0")) sReturn.remove(sReturn.length()-1,1); if(sReturn.endsWith(".")) sReturn.remove(sReturn.length()-1,1); } return sReturn; }But, this is successively chaining a lot of string operations. The previously mentions methods are probably better.
@J.Hilk
Thank you for the code.
honestly, I solved the issue two or three days ago. When I found I can't rely on a function offered by Qt on this specific problem, I returned to my old friend, C++, and solved the issue using it.
But I appreciate your paying attention to the problem.
