Stack Overflow when declaring array

Hello,

I have a class, MyClass, which contains a 2-dimensional array, my_array, of a structure of type MyStruct. Below is the code I have used to implement this :

Code:

---

struct MyStruct
{
    int u;
    int v;
    int w;
    int x;
    int y;
    int z;
};

class MyClass
{
private:
    MyStruct my_array[1000][500];
};

void main()
{
    MyClass my_class;
}

---

However, when I compile this, I get a compiler error indicating "stack overflow". I'm a bit of a rookie, but from what I gather this is because when I create the my_struct array, I am creating it directly onto the stack, rather than the heap. And, seeing as my_struct contains a large number of MyStructs, each of which contains 6 ints, then that is a lot of data to be stored on the stack, causing an overflow.

But I don't know how to do this any other way, and I don't really understand which elements of the program are created in the stack, and which are created on the heap.

I have tried defining MyClass without telling it to explicitely create all of the elements of the array:

Code:

---

class MyClass
{
private:
    MyStruct my_array[][];
};

---

But I get the error: "error C2087: 'my_array' : missing subscript"

All I want to do is let my program know that this array will exist, but I don't need to create all the elements of the array right at the start of the program do I? And they certainly shouldn't be put on the stack, as I will need to refer to them throughout the program...

This whole stack / heap thing is getting me down, please could

An array of this size needs to be allocated dynamically. That's what std::vector is for:

Code:

---

#include <vector>

std::vector<std::vector<MyStruct> > my_array;

---

Quote:

---

Originally Posted by ejohns85

All I want to do is let my program know that this array will exist, but I don't need to create all the elements of the array right at the start of the program do I? And they certainly shouldn't be put on the stack, as I will need to refer to them throughout the program...

---

One possibility is to #include <vector> and then change your MyClass definition to:

Code:

---

class MyClass
{
public:
    MyClass() : my_array(1000, std::vector<MyStruct>(500)) {}
private:
    std::vector<std::vector<MyStruct> > my_array;
};

---

By the way, void main should be int main.

Any direct array declaration in a function does indeed use stack-space. That's the whole point of using such declarations (no need to call new or delete to arrange cleanup, etc).

Since 500 * 1000 elements of 6 integers is likely to be 4 * 6 * 500 * 1000 = ~12MB of space, it will overflow the stack. The normal size of stack is 1-4MB - it can be made larger, but likely is that you do not want to use stack-space for such variables anyways.

--
Mats