How to assign values to multidimensional QList

[emazed]

Hello.

I have defined QList<Qlist<QList<Qvariant>>> lst empty container, and i want to create a structure similiar to a c array, as v[10][5][8]. How can i put values into QLists?? my idea was

for (i=0; i< 10; i++) {
 for (j=0; j<5; j++) {
  for (k=0;k<8; k++) {
   lst[i][j][k] = my_value;
  }
 }
}

but is not working, how can i solve that?

Kind Regards
emazed

[emazed]

ok Qt Help says:
T &QList::operator[](int i)

Returns the item at index position i as a modifiable reference. i must be a valid index position in the list (i.e., 0 <= i < size()).

so the element must exists before i can copy a value in it. ok

[jsulm]

@emazed said in How to assign values to multidimensional QList:

but is not working

In what way it's not working?

[emazed]

@jsulm i receive a Signal Abort, and the message is index out of range.
I understand that the lst is empty, what s the proper way to do it?

[emazed]

ok Qt Help says:
T &QList::operator[](int i)

Returns the item at index position i as a modifiable reference. i must be a valid index position in the list (i.e., 0 <= i < size()).

so the element must exists before i can copy a value in it. ok

[Pl45m4]

@emazed said in How to assign values to multidimensional QList:

i want to create a structure similiar to a c array, as v[10][5][8]

Just a note:

Note: QVector and QVarLengthArray both guarantee C-compatible array layout.
QList does not. This might be important if your application must interface with a C API.

(https://doc.qt.io/qt-5/qlist.html#details)

[JonB]

@emazed said in How to assign values to multidimensional QList:

so the element must exists before i can copy a value in it. ok

Yes you must create the elements for each dimension before you can address them. A C array v[10][5][8] is pre-sized to hold all the elements. QList does not offer a "set/re-size" method at Qt5 (so you have to append), though it does at Qt6. QVector has always had a resize(). You could use resize() to create elements/make it more like the C array. Although it's not an issue at Qt6, I would use a QVector rather than a QList if i wanted to approximate the C.