I have to write a small QT program that reads in 3 mark percentages separated by commas and then do some further calculations on the marks... I have to use QInputDialog to do this but it seems like it's only possible to read in one value at a time.
at this stage I am only trying to read in and display the three marks.
When I run this code QTCreator stops working and I have to end the process in task manager.
Any idea how I can approach this would be much appreciated. Should I read in a string and then convert that to double values or is there a simpler way?
Thanks in advance.
Code:
#include <QTGui>
#include <QApplication>
#include <QString>
#include <QTextStream>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QTextStream cin(stdin, QIODevice::ReadOnly);
QTextStream cout(stdout, QIODevice::WriteOnly);
double mark1, mark2, mark3;
double passMarkNeeded = 0;
QInputDialog::getDouble(0, "Enter marks", "Marks", 1);
cin >> mark1 >> mark2 >> mark3;
cout << "User entered " << mark1 << mark2 << mark3;
return EXIT_SUCCESS;
}
Obviously you cannot use QInputDialog::getDouble because it won't allow you to input 3 values separated by commas. You should use QInputDialog::getText, QString::split and QString::toDouble:
QStringList list = QInputDialog::getText(0, "Input values", "Input values:").split(",");
if (list.count() == 3) {
double a = list[0].toDouble(),
b = list[1].toDouble(),
c = list[2].toDouble();
qDebug() << "Values:" << a << b << c;
}
I'm not sure why you use QInputDialog and the standard input (cin). QInputDialog is for GUI apps, and cin is console apps. It's strange and pointless to use them together in such a way.
Related
Сan someone explain to me results of this test program?
#include <QApplication>
#include <QDebug>
#include <QFontMetrics>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QFont font;
font.fromString("Monospace,14");
QFontMetrics fm(font);
qDebug() << "W : " << fm.width('W');
qDebug() << "8*W : " << 8*fm.width('W');
qDebug() << "WWWWWWWW: " << fm.width("WWWWWWWW"); // 8*W
return 0;
}
After comipiling this code with Qt5.11 I have such results:
W : 11
8*W : 88
WWWWWWWW: 92
Size of one character 'W' for this monospace font is 11. I expect that size of string that consists of 8 such characters should be 88. But QFontmetrics::width returns 92!
The problem was in rounding. If I use QFontMetricsF instead of QFontMetrics results are correct
W : 11.4375
8*W : 91.5
WWWWWWWW: 91.5
But I found another strange thing. QFontMetricsF::maxWidth() should returns qreal type, but in fact it always returns rounded value (11 in my example). It looks like bug in Qt.
https://bugreports.qt.io/projects/QTBUG/issues/QTBUG-73458?filter=allopenissues
I have no idea why, but i can´t get the simplest example of QTemporaryFile to run... My real intent is to write data from QAudioInput into a temporary file before it is processed later.
After trying several times I realized that neither .read(), .readLine(), .readAll() or .write() would have any effect... The error string is always "Unknown Error" and it neither works for QFile or QTemporaryFile.
#include <QCoreApplication>
#include <QTemporaryFile>
#include <QDebug>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QTemporaryFile tf;
tf.open();
tf.write("Test");
QTextStream in(&tf);
qDebug() << "Testprogramm";
qDebug() << tf.isOpen();
qDebug() << tf.errorString();
qDebug() << in.readLine();
qDebug() << tf.readAll();
tf.close();
return a.exec();
}
The debug posts:
Testprogramm
true
"Unknown error"
""
""
Thank you in advance!
You need to move the file pointer back to the beginning of the file. This has to be done on the file itself when there's no stream on the file, or using the stream when one exists. Also - QFile is a proper C++ class that manages the file resource. There's no need to manually close the file. QFile::~QFile does that job.
The following works just fine:
#include <QtCore>
int main() {
auto line = QLatin1String("Test");
QTemporaryFile tf;
tf.open();
Q_ASSERT(tf.isOpen());
tf.write(line.data());
tf.reset(); // or tf.seek(0)
QTextStream in(&tf);
Q_ASSERT(in.readLine() == line);
in.seek(0); // not in.reset() nor tf.reset()!
Q_ASSERT(in.readLine() == line);
}
The above also demonstrates the following techniques applicable to sscce-style code:
Inclusion of entire Qt module(s). Remember that modules include their dependencies, i.e. #include <QtWidgets> is sufficient by itself.
Absence of main() arguments where unnecessary.
Absence of QCoreApplication instance where unnecessary. You will get clear runtime errors if you need the application instance but don't have one.
Use of asserts to indicate conditions that are expected to be true - that way you don't need to look at the output to verify that it is correct.
Use of QLatin1String over QStringLiteral where ASCII strings need to be compared to both C strings and QStrings. Implicit ASCII casts can be a source of bugs and are discouraged.
QLatin1String is a constant (read-only) wrapper, designed to wrap C string literals - thus there's no need to make line additionally const, although in real projects you'd want to follow the project's style guide here.
I'm making a simple Qt app that reads stuff from a CSV file and generates a PCAP data file out of it for reading by some other software.
And so soon as I invoque pcap_open_dead, pcap_dump_open or pcap_dump, I get no more console output upon running my small converter. Even the Hello World that comes at the beginning of the main doesn't show up any more. From the code below, if I simply comment out those three methods, the console output and "Hello World" come back.
Being new and therefore clueless about pcap, I ask for help.
#include <QCoreApplication>
#include <iostream>
#include "pcap.h"
using namespace std;
struct pcapWriter_S
{
bool isAvailable;
int m_OutPcapIpId;
pcap_t* m_OutPcapHandle;
pcap_dumper_t* m_OutPcapFile;
}m_pcapWriter;
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
cout << "Hello World!" << endl;
//m_pcapWriter.m_OutPcapHandle = pcap_open_dead(DLT_EN10MB,65535);
//m_pcapWriter.m_OutPcapFile = pcap_dump_open(m_pcapWriter.m_OutPcapHandle, QString("tmp_csv_out.pcap").toAscii().data());
m_pcapWriter.m_OutPcapIpId = 1;
if (m_pcapWriter.m_OutPcapFile != 0)
{
m_pcapWriter.isAvailable = true;
}
QByteArray pkt_data;
// Omitted code to generate pkt data from input file
m_pcapWriter.m_OutPcapIpId++;
//pcap_dump((unsigned char*)m_pcapWriter.m_OutPcapFile, &header, (unsigned char*)pkt_data.data());
return a.exec();
}
Somehow this was due to me calling pcap_open but not pcap_close quite yet. In between console stuff gets lost - can't swear it gets written on the pcap thing but it blocks the console anyway.
I have rich text items implemented using QGraphicsTextItem
To set font size, for example:
void set (int fontSize) {
QTextCursor _cursor = textCursor();
QTextCharFormat _format;
_format.setFontPointSize(fontSize);
_cursor.mergeCharFormat(_format);
setTextCursor(_cursor); }
A lot more complicated is to read the font size.
Assuming I have a selection, I must iterate through the document, through all QTextBlock, QTextFragment, reading the QTextCharFormat ...
But the simple option, if there is no selection, just reading the font size at cursor:
int get () {
return textCursor().charFormat().fontPointSize(); }
This works, but I found 3 issues:
1) Setting font size by QGraphicsTextItem properties:
QFont f = font();
f.setPointSize(20);
setFont(f);
this returns 0 by my get function above. To set the font size for the entire item, I have to use the same method as in the set function.
Shouldn't the setFont method set a font that can be read from the QTextCursor ?
2) setHtml can set formatting - but I don't see any way to read that formatting
How can I read the rich text formatting from an html fragment ? Is the only posiblity, parsing the html ?
3) (my current stumbling block)
Copy formatted text from an outside source and paste in the QGraphicsTextItem seems to maintain the formatting of the source - but how can I read that formatting ?
The get method above reads font size 0 if the text was pasted from outside.
font().pointSize() always returns 8. (I have not set it so I imagine that is a default)
Is there another method to read the text format ?
is the clipboard text formatted using html ?
How can I find the font size (or any other formatting) from the pasted text ?
(The same questions apply to block formatting, like alignment).
I think most of your problems could be solved by getting the QTextDocument for your QGraphicsTextItem object and work with it. QTextDocument and its methods (like QTextFormat::property(int propertyId)) can help you to get a lot of properties for your text.
1) If you set the size using the QFont object, you should get the size using the same way.
2) When you set the text using html, QGraphicsTextItem::font() is not useful so you need to get the QTextDocument and use their functions instead.
3) Same as 2. I think... because I don't have your code to test it :)
Well, here you have a code as an example. I hope this answer helps you.
#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsTextItem>
#include <QTextCursor>
#include <QTextCharFormat>
#include <QFont>
#include <QDebug>
#include <QTextDocument>
#include <QTextBlock>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QGraphicsScene scene;
QGraphicsView view(&scene);
/* ITEM 1 */
QGraphicsTextItem* item_1 = new QGraphicsTextItem("QGraphicsTextItem 1");
item_1->setTextInteractionFlags(Qt::TextEditorInteraction);
QFont f = item_1->font();
f.setPointSize(30);
item_1->setFont(f);
qDebug() << "textCursor().position() (returns 0): " <<
item_1->textCursor().position();
qDebug() << "textCursor().charFormat().fontPointSize() (returns 0): " <<
item_1->textCursor().charFormat().fontPointSize();
qDebug() << "font().pointSize() (returns 30 - OK!): " <<
item_1->font().pointSize();
QTextDocument* doc = item_1->document();
f = doc->defaultFont();
qDebug() << "pointSize (returns 30 - OK!): " << f.pointSize();
scene.addItem(item_1);
/* ITEM 2 */
QGraphicsTextItem* item_2 = new QGraphicsTextItem();
item_2->setPos(0, 50);
item_2->setHtml("<html><head/><body><p>"
"<span style=\"font-size:14pt; font-weight:600;\">QGraphics</span>"
"<span style=\"font-size:24pt; font-weight:600;\">TextItem 2</span>"
"</p></body></html>");
qDebug() << "font().pointSize() (returns 8, the default value): "
<< item_2->font().pointSize();
doc = item_2->document();
f = doc->defaultFont();
qDebug() << "pointSize (returns 8, the default value): " << f.pointSize();
QVector<QTextFormat> formats = doc->allFormats();
QVectorIterator<QTextFormat> i(formats);
while (i.hasNext()) {
QTextFormat format = i.next();
if (format.property(QTextFormat::FontPointSize).isValid())
qDebug() << "format.property (returns 14 or 24): " <<
format.property(QTextFormat::FontPointSize).toInt();
}
/*
* Get the block of text. In this example, we only have one block, but
* two text fragments (see below)
*/
QTextBlock text_block = item_2->document()->findBlock(1);
QTextBlock::iterator it;
for (it = text_block.begin(); !(it.atEnd()); ++it) {
QTextFragment currentFragment = it.fragment();
if (currentFragment.isValid())
qDebug() << "currentFragment.text(): " << currentFragment.text();
qDebug() << "currentFragment.charFormat().font().pointSize() "
"(returns 14 or 24, depending on"
"the current text fragment): " <<
currentFragment.charFormat().font().pointSize();
}
scene.addItem(item_2);
view.setFixedSize(640, 480);
view.show();
return a.exec();
}
I've looked around a little bit but couldn't find an answer to this.
I have a function returning a pair of pointers to objects, the situation can be simplified to:
#include <iostream>
#include <utility>
#include <memory>
std::pair<int *, int *> shallow_copy()
{
int *i = new int;
int *j = new int;
*i = 5;
*j = 7;
return std::make_pair(i, j);
}
int main(int argc, char *argv[])
{
std::pair<int *, int *> my_pair = shallow_copy();
std::cout << "a = " << my_pair.first << " b = " << *my_pair.second << std::endl;
// This is just creating a newpointer:
std::unique_ptr<int> up(my_pair.first);
std::cout << "a = " << &up << std::endl;
delete my_pair.first;
delete my_pair.second;
return 0;
}
I cannot change the return value of the function. From std::cout << "a = " << &up << std::endl; I can see that the address of the smart pointer is different from the address of the raw pointer.
Is there a way to capture tha std::pair returned by the function in a std::unique_ptr and prevent memory leaks without calling delete explicitly?
NB: The question have been edited to better state the problem and make me look smarter!
You're doing it the right way, but testing it the wrong one. You're comparing the address in first with the address of up. If you print up.get() instead (the address stored in up), you'll find they're equal.
In addition, your code has a double-delete problem. You do delete my_pair.first;, which deallocates the memory block pointed to by my_pair.first and also by up. Then, the destructor of up will deallocate it again when up goes out of scope, resulting in a double delete.
You also asked how to capture both pointers in smart pointers. Since the constructor of std::unique_ptr taking a raw pointer is explicit, you cannot directly do this with a simple std::pair<std::unique_ptr<int>, std::unique_ptr<int>>. You can use a helper function, though:
std::pair<std::unique_ptr<int>, std::unique_ptr<int>> wrapped_shallow_copy()
{
auto orig = shallow_copy();
std::pair<std::unique_ptr<int>, std::unique_ptr<int>> result;
result.first.reset(orig.first);
result.second.reset(orig.second);
return result;
}
Now, use wrapped_shallow_copy() instead of shallow_copy() and you will never leak memory from the call.