this is weird...

harry

hi.
something weird is going on.
i have a couple of lines that assign colors to an array. someting like this:

myColor[0] = new QColor( 0, 0, 0);

the weird thing is that when i comment those lines out, the program quits normally when i click the close button of the window. but when i DON'T comment those lines out, when i click that close button, i get the following error, in red:

The program has unexpectedly finished.

and the qt creator informs me that the program crashed. i dont understand whats going on here. am i doing somethiong wrong?

mrjj

well what do you with myColor ?
just inserting pointers to QColor in a list should not crash anything.

how did you define myColor ?

QColor *myColor[100];

is it global data ?

if you defined it in a function, then it will run out of scope and be invalid later.

harry

@mrjj said:

well what do you with myColor ?
just inserting pointers to QColor in a list should not crash anything.

right now i don't do anything with it. the plan is to provide a set of colors for all UI elements to use, accessible via a function.

how did you define myColor ?
QColor *myColor[100];

i use QColor *myColor[];
should there be a number between [ and ] ?

is it global data ?

the QColor *myColor[]; line is in the header file, just after the Q_OBJECT line. that should make it available to all the functions of the class, right?

if you defined it in a function, then it will run out of scope and be invalid later.

the assignments are in a function, but the definition is in the header file

yoavmil

a tip for debuging this: run in debug mode, with the debugger turned on, see where the crash happens, and fugure it out.
looks like something is trying to delete it layer, maybe twice.
for a design tip, try as much as you can not to use new and delete, unless you must need it. Qt has its QObect way to make sure you don't forget to delete things. QColor is just an integer, so there is no need to make it dynamic memory.

SGaist

Hi,

You are declaring a pointer to an array of QColor objects, did you allocated before using it ? If you need a list/vector of QColor why not use QVector<QColor> or std::vector<QColor> ?

@yoavmil QColor is not just an integer, it's a full class of its own. Using QObject when needed doesn't free you from proper memory management handling.

mrjj

@harry
--should there be a number between [ and ] ?
yes if you mean it to be a list. else/now
it means a pointer to a list.
as @SGaist mentions, it might be easier to use a dynamic list instead of old type of c array
so std::vector<QColor *> MyColor;
and MyColor.push_back( new QColor( 0, 0, 0) );
Note that the vector wont delete the the QColors object.

--that should make it available to all the functions of the class, right?
Yes, it is a so called member variable and is the correct way to have data.

--the plan is to provide a set of colors for all UI elements to use
Can I ask why stylesheets wont work for you ?
http://doc.qt.io/qt-5.5/stylesheet-examples.html
You can easy say for all Buttons, use this color.
If you apply it to mainwindow, it applies to all objects on screen.

SGaist

To add to @mrjj, allocating QColor on the heap is rather unusual, if you take a look at Qt's classes which are using QColor, you'll see they all take const references. So you'll be dereferencing your heap allocated objects all the time if you use them with Qt classes which essentially wastes CPU cycles.

harry

i finally had some time to return to this project, and now i have 2 more problems:

as i said above, i have an array of QColors. the problem is that when i try to access one of them with

return mycolor[n];

the compiler gives me the following error:

invalid conversion from QColor* to Qrgb.

wait, what? where does this Qrgb come from? the array contains Qcolors, and the function (or method?) is supposed to return a QColor. so what am i doing wrong here?

the other problem is that the paintEvent() function of that class is not called. i change the size (both by dragging the edge of the window and by calling resize()), i call update() but paintEvent does not run, the background does not turn green, and the breakpoint is not hit. what's going on here? it is a subclass of QWidget, in case that matters.

SGaist

You don't have an array of QColor, you have an array of QColor pointers. Since your function returns a QColor object, a conversion must be done and the constructor that matches best is the one taking a Qrgb, but still, it's not valid.

As suggested before, use a vector of QColor rather than a vector of pointers to QColor.

As for paintEvent, can you post your code ?

harry

@SGaist said:

You don't have an array of QColor, you have an array of QColor pointers. Since your function returns a QColor object, a conversion must be done and the constructor that matches best is the one taking a Qrgb, but still, it's not valid.

As suggested before, use a vector of QColor rather than a vector of pointers to QColor.

i put in a QVector, nd now it seems to work ok. i'm gonna find out when i get to the point where i get the button to request a color from the screen.

As for paintEvent, can you post your code ?

what code are you referring to? the code in my paintEvent() method is irrelevant right now because it does not get called. yes, i have confirmed that by setting a breakpoint on the first line.

my main() method looks like this:

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MyScreen w;
w.show();
return a.exec();
}

did i mention that the paintEvent() problem is with MyScreen?

in myscreen.h i had these lines:

public slots:
void paintEvent();

and then i saw these lines in an example program:

protected:
void paintEvent();

and i tried them out but that change made no difference.

Jakob

@harry You should read, learn, and remember this: http://www.cplusplus.com/doc/tutorial/arrays/

SGaist

Your paintEvent signature is wrong, it's missing the parameter.

harry

@harry said:

@SGaist said:

You don't have an array of QColor, you have an array of QColor pointers. Since your function returns a QColor object, a conversion must be done and the constructor that matches best is the one taking a Qrgb, but still, it's not valid.

As suggested before, use a vector of QColor rather than a vector of pointers to QColor.

i put in a QVector, nd now it seems to work ok. i'm gonna find out when i get to the point where i get the button to request a color from the screen.

ok, i'm trying to access that array now, and when i say something like

Qcolor c = MyColor[index];

i get a little window with an error message about a segmentation fault.

this line is in the header:

QVector<QColor> MyColor;

what am i doing wrong?

mrjj

Hi
QVector<QColor> MyColor;
means, dynamic list of colors. (it just defines it)
But unless do you
MyColor.append( QColor(255,0,0) );

Then
Qcolor c = MyColor[index];
will crash your program as the list is empty.

harry

@mrjj said:

Hi
QVector<QColor> MyColor;
means, dynamic list of colors. (it just defines it)
But unless do you
MyColor.append( QColor(255,0,0) );

i guess i should have mentioned that i have a couple of lines like this:

MyColor[3] = QColor( 0, 255, 255);

in my initcolors method. and i have confirmed that this method gets called when i launch the app, and it assigns the colors as intended.

should i try the append thing instead? but then how can i be sure which color ends up at which index?

mrjj

hi
if u have
MyColor[3] = QColor( 0, 255, 255);
then list is not empty
maybe index just too high for what u got in list.
use the .size() to check if index is ok

harry

@mrjj said:

hi
if u have
MyColor[3] = QColor( 0, 255, 255);
then list is not empty
maybe index just too high for what u got in list.
use the .size() to check if index is ok

just checked: size is 10 as it should be
index is 1, well within limits.

mrjj

but did u do
MyColor[0] = QColor( 0, 255, 255);
MyColor[1] = QColor( 0, 255, 255);
MyColor[2] = QColor( 0, 255, 255);
MyColor[3] = QColor( 0, 255, 255);
MyColor[4] = QColor( 0, 255, 255);
etc
does it have one at 1 ?

update:
if I do
QVector<QColor> colors;
colors[0]= QColor(244,0,0); <<< crash here.
qDebug() << colors.size();

So not sure why it seems to work for you.
But if u have size() 10 then it must have.
I would use append.
just append in the order you want.

harry

@mrjj said:

but did u do
MyColor[0] = QColor( 0, 255, 255);
MyColor[1] = QColor( 0, 255, 255);
MyColor[2] = QColor( 0, 255, 255);
MyColor[3] = QColor( 0, 255, 255);
MyColor[4] = QColor( 0, 255, 255);
etc
does it have one at 1 ?

yes, i fill the array with 10 different colors.

update:
if I do
QVector<QColor> colors;
colors[0]= QColor(244,0,0); <<< crash here.
qDebug() << colors.size();

So not sure why it seems to work for you.
But if u have size() 10 then it must have.
I would use append.
just append in the order you want.

i tried append. it seems to work, but i still have the same problem: when i try to get a qcolor from the qvector like this:

return myColor.at(1);

i get that little window with the segmentation fault. SIGSEGV, if that makes a difference.

i just thought of something. gotta try it out...

harry

@harry said:

i just thought of something. gotta try it out...

i have all my mycolor.append() lines in initColors(), and there they work nomally. but when i copy one of them into getColor(), i get a segmentation fault. i guess that means initColors() can access the QVector but getColor() can not. question is, why? both methods (or functions or whatever) are part of the same class, so what's going on here? weird.