C++ – Class members created on stack or heap

cclassheap-memorystack-memory

Need to know if such a 3d matrix would be created in the stack or on the heap and if its on the stack how to new it and initialize default values correctly (memset)

class Matrix {
     protected:
         int n[9000][420]; // is stack or heap if VVV is pointer?
};

void main()
{
         Matrix* t = new Matrix(); // created on heap
}

Best Answer

It all comes down to how you create the parent object.

MyClass {
    int n[10];
};

int main(...) {
    MyClass *c1 = new MyClass; // everything allocated on heap, 
                               // but c1 itself is automatic
    MyClass c2;                // everything allocated on stack
    // ...
}

Heaps and stacks are of course an implementation detail, but in this case I think it's fair to specify.

Related Solutions

C++ – When should you use a class vs a struct in C++

The differences between a class and a struct in C++ is:

struct members and base classes/structs are public by default.
class members and base classes/struts are private by default.

Both classes and structs can have a mixture of public, protected and private members, can use inheritance and can have member functions.

I would recommend you:

use struct for plain-old-data structures without any class-like features;
use class when you make use of features such as private or protected members, non-default constructors and operators, etc.

Python – Are static class variables possible in Python

Variables declared inside the class definition, but not inside a method are class or static variables:

>>> class MyClass:
...     i = 3
...
>>> MyClass.i
3

As @millerdev points out, this creates a class-level i variable, but this is distinct from any instance-level i variable, so you could have

>>> m = MyClass()
>>> m.i = 4
>>> MyClass.i, m.i
>>> (3, 4)

This is different from C++ and Java, but not so different from C#, where a static member can't be accessed using a reference to an instance.

See what the Python tutorial has to say on the subject of classes and class objects.

@Steve Johnson has already answered regarding static methods, also documented under "Built-in Functions" in the Python Library Reference.

class C:
    @staticmethod
    def f(arg1, arg2, ...): ...

@beidy recommends classmethods over staticmethod, as the method then receives the class type as the first argument, but I'm still a little fuzzy on the advantages of this approach over staticmethod. If you are too, then it probably doesn't matter.

Best Answer

Related Solutions

C++ – When should you use a class vs a struct in C++

Python – Are static class variables possible in Python

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