Got segfault on a macbook pro with a 24+bits indexed array

Question

I am using GCC + the terminal to make an array of prime numbers.

I once asked on #[email protected], but I still don't understand:

An int can store values on 32 bits (so a total of 2^32 unique values), but can't an array have more than 2^24 values ?

I'm not sure, but is http://stackoverflow.com/questions/2318278/why-24-bits-registers already answers my question ?

And does that mean that making an array of long int doesn't solve the problem ? Is there some (proportionately fast) way I can bypass this, like using an int[][] to store those numbers ? Or maybe an include or lib to use an arbitrary number of bytes to store numbers ?

    int main()  
    {  
        int array1[160000];  
        printf("first array declared fine.\n");  
        int array2[170000];  

        int array3[1600000];  
        printf("first array declared fine.\n");  
        int array4[1700000];  

        int array5[16000000];  
        printf("first array declared fine.\n");  
        int array6[17000000];  
    }

Answer 1

Since you are creating your arrays on the stack, I suppose your segfault is caused by a stack overflow. I would suggest creating such big arrays on the heap, like this:

int* array = malloc(17000000 * sizeof(int));

So the reason that you get a segfault has nothing to do with using indexes larger than 2^24 but with the fact that the size of all your arrays combined is larger than the size of the stack, causing a stack overflow.