Set QLineEdit to accept numbers only

Question

I have a QLineEdit where the user should enter only numbers.

So, is there only a numeric value for QLineEdit ?

Answer 1

QLineEdit::setValidator() , for example:

 myLineEdit->setValidator( new QIntValidator(0, 100, this) ); 

or

 myLineEdit->setValidator( new QDoubleValidator(0, 100, 2, this) ); 

See: QIntValidator , QDoubleValidator , QLineEdit :: setValidator

Answer 2

Best QSpinBox .

And for double value use QDoubleSpinBox .

 QSpinBox myInt; myInt.setMinimum(-5); myInt.setMaximum(5); myInt.setSingleStep(1);// Will increment the current value with 1 (if you use up arrow key) (if you use down arrow key => -1) myInt.setValue(2);// Default/begining value myInt.value();// Get the current value //connect(&myInt, SIGNAL(valueChanged(int)), this, SLOT(myValueChanged(int))); 

Answer 3

You can also set inputMask :

 QLineEdit.setInputMask("9") 

This allows the user to enter only one digit from 0 to 9 . Use multiple 9 to allow the user to enter multiple numbers. See also a complete list of characters that can be used in the input mask .

(My answer is in Python, but it's hard to convert to C ++)

Answer 4

Why aren't you using QSpinBox for this purpose? You can set the invisible up / down buttons with the following line of codes:

 // ... QSpinBox* spinBox = new QSpinBox( this ); spinBox->setButtonSymbols( QAbstractSpinBox::NoButtons ); // After this it looks just like a QLineEdit. //... 

Answer 5

Regex validator

So far, other answers provide solutions only for a relatively limited number of numbers. However, if you are interested in an arbitrary or variable number of digits, you can use the QRegExpValidator , passing a regular expression that accepts only digits (as noted in user2962533's comment). Here is a minimal, complete example:

 #include <QApplication> #include <QLineEdit> #include <QRegExpValidator> int main(int argc, char *argv[]) { QApplication app(argc, argv); QLineEdit le; le.setValidator(new QRegExpValidator(QRegExp("[0-9]*"), &le)); le.show(); return app.exec(); } 

QRegExpValidator has its advantages (and this is only an understatement). It allows many other useful checks:

 QRegExp("[1-9][0-9]*") // leading digit must be 1 to 9 (prevents leading zeroes). QRegExp("\\d*") // allows matching for unicode digits (eg for // Arabic-Indic numerals such as ٤٥٦). QRegExp("[0-9]+") // input must have at least 1 digit. QRegExp("[0-9]{8,32}") // input must be between 8 to 32 digits (eg for some basic // password/special-code checks). QRegExp("[0-1]{,4}") // matches at most four 0s and 1s. QRegExp("0x[0-9a-fA-F]") // matches a hexadecimal number with one hex digit. QRegExp("[0-9]{13}") // matches exactly 13 digits (eg perhaps for ISBN?). QRegExp("[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}") // matches a format similar to an ip address. // NB invalid addresses can still be entered: "999.999.999.999". 

Learn more about online editing behavior.

According to the documentation :

Please note that if a validator is installed in the edit line, the returnPressed () / editFinished () signals will only be sent if the validator returns QValidator :: Acceptable.

Thus, editing the line will allow the user to enter numbers, even if the minimum amount has not yet been reached. For example, even if the user did not enter text against the regular expression "[0-9]{3,}" (which requires at least 3 digits), editing the line still allows the user to enter input to achieve this minimum requirement. However, if the user finishes editing, not satisfying the requirement of "at least 3 digits", the input will be incorrect; the returnPressed() and editingFinished() signals will not be emitted.

If the regular expression has a maximum boundary (for example, "[0-1]{,4}" ), then editing the line will stop any input after 4 characters. In addition, for character sets (ie, [0-9] , [0-1] , [0-9A-F] , etc.) Line editing allows you to enter only characters from this particular set.

_{Note that I only tested this with Qt 5.11 on macOS, and not on other versions of Qt or operating systems. But given the cross-platform Qt scheme ...}

_{Demo: Regex Validators Showcase}

Answer 6

If you are using QT Creator 5.6, you can do it like this:

 #include <QIntValidator> ui->myLineEditName->setValidator( new QIntValidator); 

I recommend that you put this line after ui-> setupUi (this);

Hope this helps.