c++ - Declare large array on Stack

Question

I am using Dev C++ to write a simulation program. For it, I need to declare a single dimensional array with the data type double. It contains 4200000 elements - like double n[4200000].

The compiler shows no error, but the program exits on execution. I have checked, and the program executes just fine for an array having 5000 elements.

Now, I know that declaring such a large array on the stack is not recommended. However, the thing is that the simulation requires me to call specific elements from the array multiple times - for example, I might need the value of n[234] or n[46664] for a given calculation. Therefore, I need an array in which it is easier to sift through elements.

Is there a way I can declare this array on the stack?

Answer 1

No there is no(we'll say "reasonable") way to declare this array on the stack. You can however declare the pointer on the stack, and set aside a bit of memory on the heap.

double *n = new double[4200000];

accessing n[234] of this, should be no quicker than accessing n[234] of an array that you declared like this:

double n[500];

Or even better, you could use vectors

std::vector<int> someElements(4200000);
someElements[234];//Is equally fast as our n[234] from other examples, if you optimize (-O3) and the difference on small programs is negligible if you don't(+5%)

Which if you optimize with -O3, is just as fast as an array, and much safer. As with the

double *n = new double[4200000]; 

solution you will leak memory unless you do this:

delete[] n;

And with exceptions and various things, this is a very unsafe way of doing things.