I have custom(dynamic QString) for example something like this 123+555 and i need to get this after +.Also there can be something different then + (/,*,- etc.). My question is how to get part of string after some char.
Use the split function, which allows you to specify the separator and returns a list of the elements.
QString string("123+555");
QStringList listItems = string.split('+', QString::SkipEmptyParts);
QString finalString = listItems[1];
Alternatively, you can find by index the separating character location and use that with a call to right
Since you're usin Qt, you could try the class: QRegExp.
With such class you could write code like this:
// This code was not tested.
QRegExp rx("(\\d+)(\\+|\\-|\\*|/)(\\d+)"); // Be aware, I recommend you to read the link above in order to see how construct the proper regular expression.
int pos = rx.indexIn("23+344");
if (pos > -1) {
QString number_1 = rx.cap(1); // "23"
QString op = rx.cap(2); // "+"
QString number_2 = rx.cap(3); // "344"
// ...
}
This way you don't have to write code to check which of the characters(operators) "+, -, *, /" is present to then perform a split on the string depending on what character was found.
Related
I have to read numbers from line edit in Qt Creator, and then divide them by 100 and display them in a label.
The only method I know is:
QString OOP_marks = ui->lineEdit_OOP_marks_input->text();
ui->label_OOP_marks->setText(QString(OOP_marks));
But the above method cannot read numbers; it reads string. I have tried a lot but can't figure out the code for this part of the program.
You can use QString::toDouble for converting string to number. If you are planning to accept integers use QString::toInt instead. To convert number to string again QString::number is way to go.
const auto& OOP_marks = ui->lineEdit_OOP_marks_input->text();
bool isNumber; // optional
const double number = OOP_marks.toDouble(&isNumber);
const auto& result = isNumber ? QString::number(number / 100) : QString("Please enter valid number.");
ui->label_OOP_marks->setText(result);
But I suggest you to use QSpinBox or QDoubleSpinBox, instead of QLineEdit.
How about QString toInt function, and then static QString::number function?
QString OOP_marks = ui->lineEdit_OOP_marks_input->text();
int OOP_marks_val = OOP_marks.toInt();
ui->label_OOP_marks->setText(QString::number(OOP_marks_val/100));
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'm working with Qt on an existing project. I'm trying to send a string over a serial cable to a thermostat to send it a command. I need to make sure the string only contains 0-9, a-f, and is no more or less than 6 characters long. I was trying to use QString.contains, but I'm am currently stuck. Any help would be appreciated.
You have two options:
Use QRegExp
Use the QRegExp class to create a regular expression that finds what you're looking for. In your case, something like the following might do the trick:
QRegExp hexMatcher("^[0-9A-F]{6}$", Qt::CaseInsensitive);
if (hexMatcher.exactMatch(someString))
{
// Found hex string of length 6.
}
Update
Qt 5 users should consider using QRegularExpression instead of QRegExp:
QRegularExpression hexMatcher("^[0-9A-F]{6}$",
QRegularExpression::CaseInsensitiveOption);
QRegularExpressionMatch match = hexMatcher.match(someString);
if (match.hasMatch())
{
// Found hex string of length 6.
}
Use QString Only
Check the length of the string and then check to see that you can convert it to an integer successfully (using a base 16 conversion):
bool conversionOk = false;
int value = myString.toInt(&conversionOk, 16);
if (conversionOk && myString.length() == 6)
{
// Found hex string of length 6.
}
I want to add a new line in this. This is my sample code:
ui->button->setText(" Tips " + "\n" + TipsCount );
This is the error it shows:
invalid operands of types 'const char [7]' and 'const char [2]' to binary 'operator+'
But when I add to label it gets appended!
ui->label->setText(name + "\n" + City );
Can someone please help me?
This is a very common problem in C++ (in general, not just QT).
Thanks to the magic of operator overloading, name + "\n" gets turned into a method call (couldn't say which one since you don't list the type). In other words, because one of the two things is an object with + overloaded it works.
However when you try to do "abc" + "de", it blows up. The reason is because the compiler attempts to add two arrays together. It doesn't understand that you mean concatenation, and tries to treat it as an arithmetic operation.
To correct this, wrap your string literals in the appropriate string object type (std::string or QString most likely).
Here is a little case study:
QString h = "Hello"; // works
QString w = "World"; // works too, of course
QString a = h + "World"; // works
QString b = "Hello" + w; // also works
QString c = "Hello" + "World"; // does not work
String literals in C++ (text in quotes) are not objects and don't have methods...just like numeric values aren't objects. To make a string start acting "object-like" it has to get wrapped up into an object. QString is one of those wrapping objects, as is the std::string in C++.
Yet the behavior you see in a and b show we're somehow able to add a string literal to an object. That comes from the fact that Qt has defined global operator overloads for both the case where the left operand is a QString with the right a const char*:
http://doc.qt.nokia.com/latest/qstring.html#operator-2b-24
...as well as the other case where the left is a const char* and the right is a QString:
http://doc.qt.nokia.com/latest/qstring.html#operator-2b-27
If those did not exist then you would have had to write:
QString a = h + QString("World");
QString b = QString("Hello") + w;
You could still do that if you want. In that case what you'll cause to run will be the addition overload for both operands as QString:
http://doc.qt.nokia.com/latest/qstring.html#operator-2b-24
But if even that didn't exist, you'd have to call a member function. For instance, append():
http://doc.qt.nokia.com/latest/qstring.html#append
In fact, you might notice that there's no overload for appending an integer to a string. (There's one for a char, however.) So if your TipsCount is an integer, you'll have to find some way of turning it into a QString. The static number() methods are one way.
http://doc.qt.nokia.com/latest/qstring.html#number
So you might find you need:
ui->button->setText(QString(" Tips ") + "\n" + QString::number(TipsCount));
I want to get QString from another QString, when I know necessary indexes.
For example:
Main string: "This is a string".
I want to create new QString from first 5 symbols and get "This ".
input : first and last char number.
output : new QString.
How to create it ?
P.S. Not only first several letters, also from the middle of the line, for example from 5 till 8.
If you do not need to modify the substring, then you can use QStringRef. The QStringRef class is a read only wrapper around an existing QString that references a substring within the existing string. This gives much better performance than creating a new QString object to contain the sub-string. E.g.
QString myString("This is a string");
QStringRef subString(&myString, 5, 2); // subString contains "is"
If you do need to modify the substring, then left(), mid() and right() will do what you need...
QString myString("This is a string");
QString subString = myString.mid(5,2); // subString contains "is"
subString.append("n't"); // subString contains "isn't"
Use the left function:
QString yourString = "This is a string";
QString leftSide = yourString.left(5);
qDebug() << leftSide; // output "This "
Also have a look at mid() if you want more control.