i've started a mobile widget project
when a button is pushed the program does some astronomical calculations and then displays the results in a ui->text edit
so, the problem is that the calculations carry out two results
i want every result on a single how can it be done
p.s: i'm using
ui->textEdit->setPlainText(text)
there are no errors at all
i've tried
"/n"
std::endl
in the "/n" it write it as is
in std::endl it says:
error:
no match for 'operator+' in 'operator+(const char*, const QString&)(((const QString&)((const QString*)(& out1)))) + std::endl'
the code is:
QString out = "Alt : "+out1+std::endl+"Az : "+out2;
For the newline try this '\n'
Something like QString out = "Alt : "+out1+'\n'+"Az : "+out2; should work.
Related
I'm trying to create a simple "To Do list" app in QT Creator while coding the part that loads and saves the list from a file I get stuck on a problem.
If you enter a string like "Do my homework" the program threads the string as it should, but when you load the program again the save file got split in words. So it gets all the entries but each word separated ("Do", "my", "homework").
What is the solution? I tried working with 'char arrays' and 'getline' but they give me nothing but errors.
Here is my code for the save and load parts:
void MainWindow::LoadList(){
std::ifstream load_file("./data.bin");
char loader[255];
while (load_file >> loader){
QString Writer = QString::fromStdString(loader);
ui->lstTaskList->addItem(Writer);
}
}
void MainWindow::SaveList(){
std::ofstream save_file("./data.bin");
for (auto i = 0; i < ui->lstTaskList->count(); i++){
QString Saver = ui->lstTaskList->item(i)->text();
std::string saver = Saver.toStdString();
save_file << saver << std::endl;
}
}
Can anyone help me with this, please?
My thanks in advance...
The anwser was using QFile and QByteArray for me, I knew about QFile but it tries using basic "std" c++ till I learned more about QT.
I am trying to print an integer alongside a string but it's not really working out and am getting confused.
int cmdSeries = 3;
Serial.println("Series : " + cmdSeries);// That's where the problem occur
In visual basic we used to do it this way:
Dim cmdSeries As Integer
Console.Writeline(""Series : {0}", cmdSeries)
So i've tried it with Serial.println but it returns this error :
call of overloaded 'println(const char [14], int&)' is ambiguous
Can anyone help my out, I want to achieve this without using any libraries and in a clean way.
There is a huge difference between Arduino String class and regular C-string.
The first one overloads addition operator, but there is almost excessive usage of dynamic memory. Mainly if you use something like:
String sth = String("blabla") + intVar + "something else" + floatVar;
Much better is just using:
Serial.print("Series : ");
Serial.println(cmdSeries);
Btw, this string literal resides in Flash and RAM memory, so if you want to force using flash only:
Serial.print(F("Series : "));
But it's for AVR based Arduinos only. This macro can save a lots of RAM, if you are using lots of literals.
EDIT:
Sometimes I use this:
template <class T> inline Print & operator<<(Print & p, const T & val) {
p.print(val);
return p;
}
// ...
Serial << F("Text ") << intVar << F("...") << "\n";
It prints each part separately, no concatenations or so.
Try this
int cmdSeries = 3;
Serial.println(String("Series : ") + cmdSeries);
I try to show a persian string in Qt:
QMessageBox msg;
QString str = "یا حسین";
msg.setText(QString::fromUtf8(str));
msg.exec();
but it shows the following error :
/home/msi/Desktop/VoMail
Project/Project/VoMail-build-desktop-Qt_4_8_1_in_PATH__System__Release/../VoMail/mainwindow.cpp:40:
error: no matching function for call to 'QString::fromUtf8(QString&)'
I want to use a string variable, and not a string directly.
How can I convert a QString variable to Utf8?
As seen here, QString::fromUtf8() does not accept an argument of type QString. You must give it a const char *, so you could rewrite it like this:
QMessageBox msg;
QString str = QString::fromUtf8("یا حسین");
msg.setText(str);
msg.exec();
its not good idea write like that
using this must be better
QString str(tr("ya hossein");
and use linguist and add persian translation file to your project http://qt-project.org/doc/qt-4.8/linguist-translators.html
and if you dont want use this, you must be sure your IDE or code editor (like qtcreator) use utf8 for saving files and just use
QString str("یا حسین");
it must be ok, i tested that so many times
I have a problem with adding an element to a QListWidget. I have build some frame with QtDesigner and then, I want to add some elements to a list in code. Even when I write:
QListWidgetItem* i = new QListWidgetItem("text");
Q_ASSERT(stepsList);
qDebug() << "before";
stepsList->addItem(i);
qDebug() << "after";
It prints only "before" and crashes with SIGSEGV. Additionaly, I managed to get such error message with this:
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff6f2a4a4 in QListWidget::count() const ()
from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
What is the reason?
Well, acceptation is needed so I'll write what was wrong:
I needed to call setupUi() first, in order to initialize the stepsList as #Timo Geusch wrote.
Solved.
I'm looking to overwrite data in a text file but all I can seem to do is append to it
mFile.open(QFile::ReadWrite)
QTextStream in(&mFile);
QString first = in.readLine(); //discard the headers
QString dataLine = in.readLine(); //headers
QStringList sql_row = dataLine.split("\t"); //first row (sake of proj only 1 row)
if(sql_row[1].isEmpty()) //no user name registered
{
QByteArray user= getenv("USERNAME"); //for windows
if(user.isEmpty())
{
user = getenv("USER"); ///for MAc or Linux
}
dataLine = dataLine.insert(dataLine.indexOf("\t")+ 1,user);
in << first << endl << dataLine << endl;
mFile.flush();
mFile.close();
Change
mFile.open(QFile::ReadWrite);
to
mFile.open(QIODevice::ReadWrite | QIODevice::Truncate | QIODevice::Text);
The QIODevice vs QFile distinction isn't necessary, but I personally favor using the base class. The Truncate flag will overwrite (i.e., delete) an existing file.
Alternatively, you can follow the other suggestion and open your text file directly using one of QTextStream's constructors. The same QIODevice::OpenMode conventions apply. This only works if mFile is a FILE object and not a QFile, which isn't the case in your example.
A couple additional notes for beginners.
Related Note 1
You didn't ask about this, but I also added the QIODevice::Text flag to ensure that newline characters get translated to/from the local encoding (plain \n vs. \r\n) when you use endl.
A really common mistake is to use \r\n AND QIODevice::Text, which results in text files with double-returns \r\r\n on Windows. Just use QIODevice::Text when opening and simply \n or endl and you'll never have this problem.
Related Note 2
Using QTextStream::endl will automatically call flush() each time. If your loop is large, use "\n" instead to prevent a slowdown unless you actually need to flush every line. The stream will automatically write to disk as its buffer gets full, or when it's closed.
QFile::close() also calls flush(), which makes your mFile.flush() at the end redundant.
Use an overloaded constructor of QTextStream:
QTextStream in(&mFile, QIODevice::ReadWrite | QIODevice::Truncate);
The QIODevice::Truncate will remove all the previous content of the file, and QIODevice::ReadWrite will open it for read and write access.