Class array

[Calwoz]

Im trying to set an array of 5 elements each with a class in, im also trying to use a construct with each one, but im a bit phased with how, ive been trying this:

  for(int i = 0; i < 4; i++){
    Box Square(30,30,20,4,1);
  }

But I just get an error, is there another way of doing this?


The error is :

15 C:\Documents and Settings\Cal\My Documents\cpp\SquareGame Recoded\main.cpp variable-sized object `Square' may not be initialized 
15 C:\Documents and Settings\Cal\My Documents\cpp\SquareGame Recoded\main.cpp no matching function for call to `Box::Box()' 

[Zhuge]

The way you are doing it looks like you are calling a constructor repeatedly on the same temporary that is destructed every time you exit the for loop. I think if you want to call the individual custom constructors you have to use new.

[Calwoz]

I tried this..

  for(int i = 0; i < 4; i++){
    Box Square[i] = new Box(30,30,20,4,1);
  }

it didnt work D:

[Disch]

Creating a Box inside a loop your first example means the Box is destroyed as soon as the loop exits. Your second example is nonsensical, as you're creating Box Square[i] which treats 'Square' like an array when it's not an array, and then assigns it a pointer (from new), when it's not a pointer.

How to do this depends on how 'Square' is defined.

If you want an array of objects on the stack:

Box Square[4] = {
    Box(30,30,20,4,1),  // assuming you want all 4 to look alike
    Box(30,30,20,4,1),  // note you cannot put this in a loop, which is why this approach is
    Box(30,30,20,4,1),  //   generally not preferable
    Box(30,30,20,4,1) };

// no cleanup necessary 

If you want an array of objects on the heap, you can't use a specific ctor (have to use the default), but you can set the properties with some kind of Set function:

Box* Square = new Box[4]; // note: default ctor only
for(int i = 0; i < 4; ++i)
  Square[i].Set(30,30,20,4,1); // call a Set function to set them up

// for cleanup:
delete[] Square;

lastly you can have an array of pointers on the stack, where the actual objects are on the heap. This allows you to use a specific ctor, but notice that cleanup is more difficult:

Box* Square[4];
for(int i = 0; i < 4; ++i)
  Square[i] = new Box(30,30,20,4,1);  // specific ctor

// for cleanup
for(int i = 0; i < 4; ++i)
  delete Square[i];

[kempofighter]

alternatively,

const int SIZE(4);
Box Square[SIZE];
std::fill(Square, Square + SIZE, Box(30,30,20,4,1)); 

[Calwoz]

whats a ctor?

[jsmith]

constructor

[Calwoz]

ah well thanks for the help guys! appreciated :D