Unable to change bools in C++ struct

mzimmers

Hi all -

Just ran across weird behavior -- my attempts to set boolean members of a C++ struct don't work in my app.

struct Schedule
{
    Q_GADGET
    QML_VALUE_TYPE(schedule)
    QML_STRUCTURED_VALUE 

    Q_PROPERTY(QString name MEMBER m_name)
    Q_PROPERTY(bool maintenance MEMBER m_maintenance)
public:
    QString m_name = QString();
    bool m_maintenance = false;
    ...

and

ColumnLayout {
    id: scheduleScreen
    property schedule newSchedule: ({})

    Component.onCompleted: {
        newSchedule.maintenance = true
        console.log("ScheduleScreen.qml: newSchedule.maintenance is " + newSchedule.maintenance)
    }
    ...

produces this output:

qml: ScheduleScreen.qml: newSchedule.maintenance is false

Same behavior with another bool value in my struct, but changing other values (such as name) works.

I also tried reducing this to a minimal example, but that worked (ugh).

Any ideas where I went wrong with this? Qt 6.5.3, Windows.

Thanks...

GrecKo

@mzimmers said in Unable to change bools in C++ struct:

bool operator ==(const Schedule &rhs) const {return true;}

If you remove this non-sensical operator== your code works as expected.

My guess is that the engine modifies a temp Schedule internally, checks the equality and assign it only if it's different. As it's always equal it won't modify it.

JoeCFD

This post is deleted!

mzimmers

@JoeCFD said in Unable to change bools in C++ struct:

newSchedule.m_maintenance = true

Doesn't change anything. Plus I'm trying to use my defined properties for access to the struct.

I added a few more property modifications, and they all seem to work except for the bool:

Component.onCompleted: {
    console.log("ScheduleScreen.qml: newSchedule is " + newSchedule)
    newSchedule.name = "xxx"
    newSchedule.m_maintenance = true
    newSchedule.timeOffset = 55
    newSchedule.timeFrame = ScheduleEnums.TIMEFRAME_DAILY;
    console.log("ScheduleScreen.qml: newSchedule is " + newSchedule)
}

produces this:

qml: ScheduleScreen.qml: newSchedule is Schedule({00000000-0000-0000-0000-000000000000}, , {00000000-0000-0000-0000-000000000000}, false, false, , START_ACTION_TURN_ON, END_ACTION_TURN_OFF, START_WHEN_TIME_OF_DAY, END_WHEN_TIME_OF_DAY, 09:00:00.000, 17:00:00.000, TIMEFRAME_WEEKLY, REPEAT_EVERY_WEEK, , , , 0, )

qml: ScheduleScreen.qml: newSchedule is Schedule({00000000-0000-0000-0000-000000000000}, xxx, {00000000-0000-0000-0000-000000000000}, false, false, , START_ACTION_TURN_ON, END_ACTION_TURN_OFF, START_WHEN_TIME_OF_DAY, END_WHEN_TIME_OF_DAY, 09:00:00.000, 17:00:00.000, TIMEFRAME_DAILY, REPEAT_EVERY_WEEK, , , , 55, )

JoeCFD

@mzimmers said in Unable to change bools in C++ struct:
Sorry I did not see you use different names in property definitions. My bad. I normally use the same name.

mzimmers

@JoeCFD no problem. But it's weird, isn't it?

JonB

@mzimmers said in Unable to change bools in C++ struct:

I also tried reducing this to a minimal example, but that worked (ugh).

This really means you need to start from such a good situation, or from a bad situation, and work towards the other. Till you can produce a "this works, and with this tiny change that does not work".

GrecKo

@mzimmers
Do a copy of your schedule before modifying it and assign it back when you are done.

mzimmers

@GrecKo this:

    Component.onCompleted: {
        var tempSchedule = newSchedule
        console.log("ScheduleScreen.qml: newSchedule is " + newSchedule)
        tempSchedule.name = "xxx"
        tempSchedule.m_maintenance = true
        tempSchedule.timeOffset = 55
        tempSchedule.timeFrame = ScheduleEnums.TIMEFRAME_DAILY;
        newSchedule = tempSchedule
        console.log("ScheduleScreen.qml: tempSchedule is " + tempSchedule)
        console.log("ScheduleScreen.qml: newSchedule is " + newSchedule)
    }

Produces this:

qml: ScheduleScreen.qml: newSchedule is Schedule({00000000-0000-0000-0000-000000000000}, , {00000000-0000-0000-0000-000000000000}, false, false, , START_ACTION_TURN_ON, END_ACTION_TURN_OFF, START_WHEN_TIME_OF_DAY, END_WHEN_TIME_OF_DAY, 09:00:00.000, 17:00:00.000, TIMEFRAME_WEEKLY, REPEAT_EVERY_WEEK, , , , 0, )
qml: ScheduleScreen.qml: tempSchedule is Schedule({00000000-0000-0000-0000-000000000000}, xxx, {00000000-0000-0000-0000-000000000000}, false, false, , START_ACTION_TURN_ON, END_ACTION_TURN_OFF, START_WHEN_TIME_OF_DAY, END_WHEN_TIME_OF_DAY, 09:00:00.000, 17:00:00.000, TIMEFRAME_DAILY, REPEAT_EVERY_WEEK, , , , 55, )
qml: ScheduleScreen.qml: newSchedule is Schedule({00000000-0000-0000-0000-000000000000}, xxx, {00000000-0000-0000-0000-000000000000}, false, false, , START_ACTION_TURN_ON, END_ACTION_TURN_OFF, START_WHEN_TIME_OF_DAY, END_WHEN_TIME_OF_DAY, 09:00:00.000, 17:00:00.000, TIMEFRAME_DAILY, REPEAT_EVERY_WEEK, , , , 55, )

So...no change. Really odd, isn't it?

mzimmers

@JonB agree completely, though I'm not sure what the next step is, given how "close to the top" this code is. It probably has something to do with how I coded my struct, but I sure can't see what might be doing this.

fcarney

@mzimmers when I get strange stuff not working I do a clean, run qmake, build. Sometimes it is just a moc issue. Not sure how that works with cmake though.

mzimmers

@fcarney tried that -- same results. Good suggestion, though.

mzimmers

OK, so I discovered something, but I don't understand it. I stepped through this in the debugger, and confirmed the problem is in the C++ side: Screenshot 2023-10-18 142850.png

Then, for lack of anything else to try, I removed the initializer in my struct:

// bool m_maintenance = false; // before
bool m_maintenance; // now

and...
Screenshot 2023-10-18 143100.png
For another test, I added this line to my c'tor:

bool m_maintenance = false;

And got the original (bad) result.

I also "changed polarity" (initialize to true; try to set to false) with the same (bad) result.

So...this problem just got a little bigger. I'm not willing to release code to the field that creates structs with uninitialized values; I need to figure out what's going on here.

EDIT: this occurs on 6.6 as well as 6.5.3.

ANY ideas, no matter how far-fetched, are welcome. Thanks...

JoeCFD

Check this out.
https://stackoverflow.com/questions/1069621/are-members-of-a-c-struct-initialized-to-0-by-default
It may not be a C++ problem. Instead it is a C problem. Struct is very C style. I even avoid using it.

mzimmers

@JoeCFD interesting article, though my issue is with modification, not initialization.

Regarding the use of structs: I suppose I could use a class, but I'd be astonished if that made a difference. I'm deliberately avoiding using QObject here, too.

JoeCFD

@mzimmers bool m_maintenance; // now
is undefined.

can you try:
bool m_maintenance{ false };
I do not know if it will make a difference.

mzimmers

@JoeCFD said in Unable to change bools in C++ struct:

@mzimmers bool m_maintenance; // now
is undefined.

I realize that, and that's not acceptable. But currently I have the options of leaving it undefined, or initializing it and (somehow) making it QML-immutable in the process.

I can't even modify it if I initialize it in QML, like this:

    property schedule newSchedule: ({ "maintenance": false })

mzimmers

@JoeCFD said in Unable to change bools in C++ struct:

can you try:
bool m_maintenance{ false };

Same (bad) result. Thanks for the suggestion, though.

JoeCFD

@mzimmers
try
class Schedule

not struct Schedule
.

mzimmers

@JoeCFD no change in behavior.

GrecKo

@JoeCFD struct is just a class where everything is public by default.