StringScanner does not find the corresponding data

[xuyisheng]

StringScanner lost data with the code below:

var content = 'xxxx[fn=4][fn=37][fn=36][fn=12][fn=26]xxxx';

var _scanner = StringScanner(content);
    while (!_scanner.isDone) {
      if (_scanner.scan(RegExp('\\[fn=(\\d+)]'))) {
        print(content.substring(_scanner.lastMatch!.start + 1, _scanner.lastMatch!.end - 1));
      }
      if (!_scanner.isDone) {
        _scanner.position++;
      }
    }

the result is :

I/flutter (25050): fn=4
I/flutter (25050): fn=36
I/flutter (25050): fn=26

but If I use this method directly：

var allMatches = RegExp('\\[fn=(\\d+)]').allMatches(content);
    for (var element in allMatches) {
      print('--${element.start}');
    }

I got the right answer：

I/flutter (25050): [fn=4]
I/flutter (25050): [fn=37]
I/flutter (25050): [fn=36]
I/flutter (25050): [fn=12]
I/flutter (25050): [fn=26]

something lost when I use StringScanner.

[jolleekin]

Please try this code

      if (_scanner.scan(RegExp('\\[fn=(\\d+)]'))) {
        print(content.substring(_scanner.lastMatch!.start + 1, _scanner.lastMatch!.end - 1));
      } else {
        _scanner.position++;
      }

Some methods move the pointer forward while others don't.

[xuyisheng]

Please try this code

      if (_scanner.scan(RegExp('\\[fn=(\\d+)]'))) {
        print(content.substring(_scanner.lastMatch!.start + 1, _scanner.lastMatch!.end - 1));
      } else {
        _scanner.position++;
      }

Some methods move the pointer forward while others don't.

It works! thank u very much~

ps: Is StringScaner more efficient than using regular expressions directly?

[jolleekin]

Looking at your code, I can say you should use RegExp directly.