Subj : Re: stack overflow before it attempts to sort 1 & 2 million int arrays
To   : comp.lang.c++,comp.programming
From : alfps
Date : Sat Aug 13 2005 02:00 am

* strotee@gmail.com attempts to implement QuickSort:
> 
> void swap(int *a,int *b)
> {
>   int t=*a; *a=*b; *b=t;
> }
> void sort(int arr[], int beg, int end)
> {
>   if (end > beg + 1)
>   {
>     int piv = arr[beg], l = beg + 1, r = end;
>     while (l < r)
>     {
>       if (arr[l] <= piv)
>         l++;
>       else
>         swap(&arr[l], &arr[--r]);
>     }
>     swap(&arr[--l], &arr[beg]);
>     sort(arr, beg, l);
>     sort(arr, r, end);
>   }
> }

This is not really a C++ question, except the reason why you get
a crash.

The reason it crashes is you do a million or so recursive calls, or possibly
an infinite number (I'm not in the mood for analyzing the details), and on
current personal computers a million is about how much stack space you have.

The reason you do a million or so recursive calls, or possibly an infinite
number, has nothing to do with C++, and figuring this out is presumably part
of your assignment (which we won't do for you!), so therefore crossposted to
[comp.programming] with follow-ups there.


XFUT: [comp.programming]

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