QRegularExpressionValidator: am I missing something?!

[agarny]

Note that I constructed the regular expression string using C++ string literal concatenation rather than your QString operators not that I expect that to be of any consequence.

Indeed, I have just replaced 'my' version with yours and, as expected, it didn't make any difference.

I say "runs fine" not "works fine" because the test string is a valid URL.

Yes, everything runs fine indeed.

Is there a reason you cannot use QUrl to do the validation work for you?

Maybe, I am not sure. The fact is that I need the user to enter the URL. So, for this, I am using QLineEdit and I thought I would validate the user's entry as he enters it. Hence, my use QRegularExpressionValidator as a validator for QLineEdit. Now, are you implying that there is a way to achieve the same using QUrl as some kind of a validator? If so, I imagine that I would need to create my own validator and make it use QUrl to do the validation?

[ChrisW67]

The behaviour I see with your original code is that the line edit stops accepting more characters after the 20th 'u' is typed (making the total string length 26). It doesn't hang, backspace works for example. Once the validator stops returning Intermediate and starts returning Invalid the characters get dropped. A quick tweak of my code, shows the validator changing its mind:

QString testString("http://");
for (int i = 0; i < 32; ++i) {
    testString += "a";
    QRegularExpressionValidator validator(re);
    int pos = 0;
    qDebug() << (i+1) << testString << validator.validate(testString, pos);
}

QString testString("http://");
for (int i = 0; i < 32; ++i) {
    testString += "a";
    QRegularExpressionValidator validator(re);
    int pos = 0;
    qDebug() << (i+1) << testString << validator.validate(testString, pos);
}

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1 "http://a" 1
2 "http://aa" 1
3 "http://aaa" 1
4 "http://aaaa" 1
5 "http://aaaaa" 1
6 "http://aaaaaa" 1
7 "http://aaaaaaa" 1
8 "http://aaaaaaaa" 1
9 "http://aaaaaaaaa" 1
10 "http://aaaaaaaaaa" 1
11 "http://aaaaaaaaaaa" 1
12 "http://aaaaaaaaaaaa" 1
13 "http://aaaaaaaaaaaaa" 1
14 "http://aaaaaaaaaaaaaa" 1
15 "http://aaaaaaaaaaaaaaa" 1
16 "http://aaaaaaaaaaaaaaaa" 1
17 "http://aaaaaaaaaaaaaaaaa" 1
18 "http://aaaaaaaaaaaaaaaaaa" 1
19 "http://aaaaaaaaaaaaaaaaaaa" 1
20 "http://aaaaaaaaaaaaaaaaaaaa" 1
21 "http://aaaaaaaaaaaaaaaaaaaaa" 0
22 "http://aaaaaaaaaaaaaaaaaaaaaa" 0
23 "http://aaaaaaaaaaaaaaaaaaaaaaa" 0
24 "http://aaaaaaaaaaaaaaaaaaaaaaaa" 0
25 "http://aaaaaaaaaaaaaaaaaaaaaaaaa" 0
26 "http://aaaaaaaaaaaaaaaaaaaaaaaaaa" 0
27 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaa" 0
28 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaaa" 0
29 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaa" 0
30 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" 0
31 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" 0
32 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" 0

1 "http://a" 1
2 "http://aa" 1
3 "http://aaa" 1
4 "http://aaaa" 1
5 "http://aaaaa" 1
6 "http://aaaaaa" 1
7 "http://aaaaaaa" 1
8 "http://aaaaaaaa" 1
9 "http://aaaaaaaaa" 1
10 "http://aaaaaaaaaa" 1
11 "http://aaaaaaaaaaa" 1
12 "http://aaaaaaaaaaaa" 1
13 "http://aaaaaaaaaaaaa" 1
14 "http://aaaaaaaaaaaaaa" 1
15 "http://aaaaaaaaaaaaaaa" 1
16 "http://aaaaaaaaaaaaaaaa" 1
17 "http://aaaaaaaaaaaaaaaaa" 1
18 "http://aaaaaaaaaaaaaaaaaa" 1
19 "http://aaaaaaaaaaaaaaaaaaa" 1
20 "http://aaaaaaaaaaaaaaaaaaaa" 1
21 "http://aaaaaaaaaaaaaaaaaaaaa" 0
22 "http://aaaaaaaaaaaaaaaaaaaaaa" 0
23 "http://aaaaaaaaaaaaaaaaaaaaaaa" 0
24 "http://aaaaaaaaaaaaaaaaaaaaaaaa" 0
25 "http://aaaaaaaaaaaaaaaaaaaaaaaaa" 0
26 "http://aaaaaaaaaaaaaaaaaaaaaaaaaa" 0
27 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaa" 0
28 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaaa" 0
29 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaa" 0
30 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" 0
31 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" 0
32 "http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" 0

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It also gets progressively slower as the string gets longer. Even with 32 'a' chars, adding ".com" will validate (you cannot do it through the line edit though). I can see no reason for this behaviour. It might be some sort of recursion limit in the regex library.

If so, I imagine that I would need to create my own validator and make it use QUrl to do the validation?

Yes. Using QUrl will only give Invalid/Valid indication, where a QRegularExpression based approach can give an Intermediate indication for hasPartialMatch().

[agarny]

I tried the validation using QUrl and it's not sufficient for what I need. As you wrote, a QRegularExpression-based approach allows for intermediate state, which is useful. Also, I noticed that QUrl is too clever when it comes to validation. I mean that it will try to correct a user's mistake if it can. Anyway, QUrl validation is not an option.

Regarding QRegularExpressionValidator, there is clearly something 'funny' going on, which is the reason I decided to create a bug report for it: https://bugreports.qt-project.org/browse/QTBUG-38034.