Hi,
Am Donnerstag, 21. April 2022, 15:55:08 CEST schrieb Sean Murphy via Interest:
> I've got an existing class that will be used in both Qt and non-Qt/non-UI
> applications. One of that functions within that class parses large text files
> with what is essentially a while(!file.eof()) loop. I'd like to add
> functionality to the class that would provide some sort of parsing status
> back to anyone using the class - for example "currently on loop X of N".
> Essentially I'd like to add the equivalent of a Qt signal.
>
> Ideas I've got so far:
> 1. Use a bunch of #ifdefs to conditionally turn this class into something
> that inherits from QObject and provide the signal. The downsides to this are
> currently this is just a POD class, and we make copies of this instances of
> this class all over the place currently. Since you can't copy QObjects, that
> would add some complexity. And then it also wouldn't be able to provide
> status back in non-Qt uses since that would be #ifdef'd out.
> 2. Modify the class to take an optional progress function pointer with a
> signature like "void progress(int currentValue, int totalLoops)", and then
> within the parsing loop, if that function pointer isn't null, call it with
> the current value and total. If the function pointer is null, the class would
> behave as it does now - silently parsing without providing any status back.
> Then whatever code is instantiating one of these classes can supply their own
> progress function.
>
> I'm curious how other people have handled something like this? Right now I'm
> leaning more toward the function pointer solution since that would work for
> both Qt and non-Qt cases. I'm sure there's other ideas I haven't considered.
The most generic and flexible interface is to only do a certain number of
iterations per function call, then the caller can do whatever is necessary
for progress reporting and could even interrupt the process, e.g.:
int lines = 0;
while(thing.canParse()) {
lines += thing.parseLines(5);
Q_EMIT parsedLines(lines);
}
This requires moving state from the function itself to the class instance,
which can be easy or hard depending on the content. Or if you can use C++20,
maybe try coroutines? Those are basically a language feature for that.
Cheers,
Fabian
> Thanks in advance!
> Sean
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