Write only float values in QLineEdit

Question

How to write in QLineEdit float numbers in range (0.0 - 5.0)? I use qregexp for such a task for example QRegExp a("([a-zA-Z]{3,30})") to write user name but have no ideas to write float numbers.

Answer 1

The best option is to use the QDoubleValidator for such task, since it will not only validate the shape of the input but also the range :

auto dv = new QDoubleValidator(0.0, 5.0, 2); // [0, 5] with 2 decimals of precision
yourLineEdit->setValidator(dv);

If you are dealing with many decimals (or if you plan to change the range to a wider one), you'd probably be interested in disabling the scientific notation:

dv->setNotation(QDoubleValidator::StandardNotation);

On the other hand, and for completeness of the answer since you asked for regular expressions, a general regex for float number is [-+]?[0-9]*\\.?[0-9]+ , so for your particular range you can try: ([0-4]?\\.[0-9]+)|(5\\.0+)|([0-5]) . Anyway, I recommend using the validator, since the regex is more difficult to scale if range changes through the project or in run-time.

Answer 2

Using a regex and breaking up the ranges, 0.0 - 5.0 would be :

[0-4]\\.\\d|5\\.0

Expanded

   #  0.0  to  4.9
   [0-4] \. \d 
|  
   #  5.0
   5 \. 0