qt qstring to double

QString str = "3.14";
bool ok;
double num = str.toDouble(&ok);
if (ok) {
    // Conversion successful
    // 'num' contains the double value of the string
} else {
    // Conversion failed
    // Handle the error here
}

1. Declare a QString variable named str and assign it the value "3.14".
2. Declare a boolean variable ok.
3. Use the toDouble() function of the QString class to convert the string str to a double value. The &ok parameter is a pointer to the ok variable, which will be set to true if the conversion is successful and false otherwise.
4. Check the value of ok. If it is true, the conversion was successful, and the variable num now holds the double value of the string. Otherwise, the conversion failed, and you can handle the error accordingly.