combine QLisdt and a simple structure

[qt_gotcha]

Most posts on this subject go way beyond what I want, and I quickly loose track.

I have a structure

typedef structure LDD_POINT{
int row;
int col;
}LDD_POINT;

typedef structure LDD_POINT{
int row;
int col;
}LDD_POINT;

To copy to clipboard, switch view to plain text mode 

in my class I define:

QList <LDD_POINT> *lddlist;

QList <LDD_POINT> *lddlist;

To copy to clipboard, switch view to plain text mode 

then with each new point in the code:

ldd_point *p = new LDD_POINT;
lddlist->append(p);

ldd_point *p = new LDD_POINT;
lddlist->append(p);

To copy to clipboard, switch view to plain text mode 

which doesn't work:
c:\Qt\2010.05\qt\include\QtCore\..\..\src\corelib\ tools\qlist.h:493: candidates are: void QList<T>::append(const T&) [with T = LDD_POINT]
c:\Qt\2010.05\qt\include\QtCore\..\..\src\corelib\ tools\qlist.h:819: void QList<T>::append(const QList<T>&) [with T = LDD_POINT]

So obviously I am doing something too simple. I don't understand the const T stuff, what is the correct format, or point me to an example...

Thanks

[Zlatomir]

That is because your list contains objects (you declare it: QList <LDD_POINT>) and you are trying to add pointers to LDDD_POINT (append(p) )

One solution is to use QList<YourStruct*>

And don't forget to iterate over the QList and delete all the pointers, that should be done after you are done working with that pointers and before the QList gets out of scope.

[qt_gotcha]

thanks, I also found in an example
QList <LDD_POINT const *> listldd;
but I do know the effect of adding the const in this case

[Zlatomir]

Short answer is that QList<TYPE const*> will contain pointers to constant TYPE objects... so that you can't modify the objects using the pointer in the QList. (but you can modify pointers to "point" elsewhere)


A longer answer can be found here (i really recommend you read it)

[wysota]

And I suggest you don't use pointers.

QList<LDD_POINT> lddlist; // no pointers
lddlist.append(LDD_POINT()); // no pointers, no "new" operator

QList<LDD_POINT> lddlist; // no pointers
lddlist.append(LDD_POINT()); // no pointers, no "new" operator

To copy to clipboard, switch view to plain text mode