When I execute following code:
bool ok = false;
QByteArray ba("fffff3");
qDebug() << ok << ba.toInt(&ok, 16) << ok;
The output is true 16777203 true,I vaguely know why.Someone can explain what is going on.What is ok's change process?
Related
I want to convert my QByteArrey into a byte pointer. I found out on the internet how to go the opposite way and i found myself struggling in finding the right way to do it... So can anyone help me please?
Use data() or constData() method.
QByteArray ba("Hello world");
char *data = ba.data();
while (*data) {
cout << "[" << *data << "]" << Qt::endl;
++data;
}
I need to extract some data from string with simple syntax. The syntax is this:
_IMPORT:[any text] - [HEX number] #[decimal number]
Therefore I created regex you can see below in the code:
//SYNTAX: _IMPORT:%1 - %2 #%3
static const QRegExp matchImportLink("^_IMPORT:(.*?) - ([A-Fa-f0-9]+) #([0-9]+)$");
QRegExp importLink(matchImportLink);
QString qtWtf(importLink.pattern());
const int index = importLink.indexIn(mappingName);
qDebug()<< "Input string: "<<mappingName;
qDebug()<< "Regular expression:"<<qtWtf;
qDebug()<< "Result: "<< index;
For some reason, that does not work, I get this output:
Input string: "_IMPORT:ddd - 92806f0f96a6dea91c37244128f7d00f #0"
Regular expression: "^_IMPORT:(.*?) - ([A-Fa-f0-9]+) #([0-9]+)$"
Result: -1
I even tried to remove the anchors ^ and $ but that didn't help and also is undesired. The annoying thing is that this regexp works perfectly if I copy the output in regex101.com, as you can see here: https://regex101.com/r/oT6cY3/1
Can anyone explain what is wrong here? Did I stumble upon Qt bug? I use Qt 5.6. Is there any workaround for this?
It seems like Qt does not recognize the quatifier *? as valid. Check the method QRegExp::isValid() againts your pattern. In my case it did not work because of this. And the documentation tells that any invalid pattern will never match.
So first thing I tried was skipping the ? which perfectly fits your provided string with all capturing groups. Here is my code.
QString str("_IMPORT:ddd - 92806f0f96a6dea91c37244128f7d00f #0");
QRegExp exp("^_IMPORT:(.*) - ([A-Fa-f0-9]+) #([0-9]+)$");
qDebug() << "pattern:" << exp.pattern();
qDebug() << "valid:" << exp.isValid();
int pos = 0;
while ((pos = exp.indexIn(str, pos)) != -1) {
for (int i = 1; i <= exp.captureCount(); ++i)
qDebug() << "pos:" << pos << "len:" << exp.matchedLength() << "val:" << exp.cap(i);
pos += exp.matchedLength();
}
And here is the resulting output.
pattern: "^_IMPORT:(.*) - ([A-Fa-f0-9]+) #([0-9]+)$"
valid: true
pos: 0 len: 49 val: "ddd"
pos: 0 len: 49 val: "92806f0f96a6dea91c37244128f7d00f"
pos: 0 len: 49 val: "0"
Tested using Qt 5.6.1.
Also note that you may set greedy evaluation using QRegExp::setMinimal(bool).
I use Qt 5.2.0 (MSVC 2010).
I added to my form in Qt a ComboBox.
Then I want to fill it with numbers:
for (i = 0; i < n; i++){
ui->tableCombo->addItem(QString::number(i));
}
When I add a first element right in the form, it successfully adds numbers. But when I leave it empty, it throws an error:
ASSERT failure in QVector::operator[]: "index out of range"
Debugger shows that error occured right in this line. And there is no QVector across the line.
After adding qDebug().
qDebug() << "readFileToStringList: msg10";
for (i = 0; i < n; i++){
qDebug() << "readFileToStringList: msg20 i = " << i;
ui->tableCombo->addItem(QString::number(i+1));
qDebug() << "readFileToStringList: msg30";
}
qDebug() << "readFileToStringList: msg40";
I get the same result
readFileToStringList: msg10
readFileToStringList: msg20 i = 0
ASSERT failure in QVector<T>::operator[]: "index out of range", file C:\Qt\Qt5.2.0\5.2.0\mingw48_32\include/QtCore/qvector.h, line 369
I had this exact problem and couldn't figure it out for a couple hours. I realized ::addItem() was triggering the indexChanged(int) signal, which I had connected to a function that was causing an out-of-range error in a container.
I would say it was possibly the problem here too, but I'm sure the OP has moved on since then. To me it isn't exactly intuitive that the indexChanged signal would be called on insertion of new items, since it doesn't actually change the currentIndex.
Hopefully if anyone else gets tripped up this will help them!
addItem() doesn't throw that error! I'm positive it's coming from another instruction in your code.
Qt documentation has an entire section on Debugging Techniques, but if you are afraid of debuggers you can use the poor's man debugger: spread several qDebug() messages before and after the instructions you think are responsible for the problem:
qDebug() << "methodX: msg10";
for (i = 0; i < n; i++){
qDebug() << "methodX: msg20 i = " << i;
ui->tableCombo->addItem(QString::number(i));
qDebug() << "methodX: msg30";
}
qDebug() << "methodX: msg40";
If the message methodX: msg30 gets printed to the screen, means that addItem() didn't cause the error.
I have the following scenario:
QProcess*p;
// later
p->start();
//later
p->terminate(); // there might be unread data in stdout
//later
p->start();
I read the process stdout. After I call p->start() the second time, could there still be unread data left in the stdout buffers from the first p->start()? That would be a problem for me. Do I need to flush the buffers or something?
Okay, I've checked the sources. The QProcess::start() method explicitly clears both output buffers, so it should be okay, at least in this sense:
void QProcess::start(const QString &program, const QStringList &arguments, OpenMode mode)
{
Q_D(QProcess);
if (d->processState != NotRunning) {
qWarning("QProcess::start: Process is already running");
return;
}
#if defined QPROCESS_DEBUG
qDebug() << "QProcess::start(" << program << "," << arguments << "," << mode << ")";
#endif
d->outputReadBuffer.clear();
d->errorReadBuffer.clear();
I still think it's a bad style to reuse the same object, though.
I'm trying to free memory after using QList, but it doesn't seem to work properly.
Here's my code:
QList<double> * myList;
myList = new QList<double>;
double myNumber;
cout << "CP1" << endl;
getchar(); // checkpoint 1
for (int i=0; i<1000000; i++)
{
myNumber = i;
myList->append(myNumber);
cout << myList->size() << endl;
}
cout << "CP2!" << endl;
getchar(); // checkpoint 2
for (int i=999999; i>0; i--)
{
myList->removeLast();
cout << myList->size() << endl;
}
cout << "CP3!" << endl;
getchar(); // checkpoint 3
delete myList;
cout << "CP4!" << endl;
getchar(); // checkpoint 4
Memory usage:
CP1: 460k
CP2:19996k
CP3:19996k
CP4:16088k
So it looks like despite removing of elements and deleting myList still large part of memory is being used. I believe there is a way to handle it but I can't find it.
Thanks in advance for any help.
Pawel
Memory manager is not required to release the memory your program has allocated. There are no problems in your deallocation.
QList is an array based list. The array expands automatically, but does not shrink automatically. Removing elements from the list does not affect the size of the array.
To trim the array down to the actual size, create a new QList and add the contents to it. Then delete the original list.
Unfortunately looks like there is no convenience method to do this, like the List.TrimExcess() in .NET.