c - Allocating A Large (5000+) Array

Question

I am working on an application were there are three possible sizes for the data entered:

• small: 1000 elements
• medium= 5000 elements
• large= 500,000 elements

The problem is that I can't allocate the large array. It seems that a size larger than 5000 is not accepted.

I get a run time error when I do the following:

long  size=1000;
char ch;
int arr[size];
ch=getch();

if(ch==..)
  size=...;

Sizes of 1000 and 5000 seem to work fine, but how can I make an array of size 500k in this way?

Answer 1

You can allocate such a big array on the heap:

int *arr;
arr = malloc (sizeof(int) * 500000);

Don't forget to check that allocation succeded (if not - malloc returns NULL).

And as pmg mentioned - since this array is not located in the stack, you have to free it once you finished working with it.