std::sort function gives "Bus error: 10"

Question

Following code gives "Bus error: 10", though it works perfectly when n is changed to 30. I REALLY do NOT see any single reason for that error. Why do you think this is happening?

#include <algorithm>
#include <cstdio>
#define MAX 100000
using namespace std;

struct suffix
{
    int cur;
};

suffix suffixes[MAX];

bool cmp(suffix a, suffix b)
{
    return (a.cur <= b.cur);
}

int main()
{
   int n = 1000;
   sort(suffixes,suffixes + n,cmp);
   return 0;
}

What platform/OS are you using? How much RAM is in your machine? — Ivan Aksamentov - Drop, Dec 05 '15 at 06:34
`sort` needs a compare function that does monotonic sorting. Change `<=` to `<` and see if that helps. See http://stackoverflow.com/questions/2385690/sorting-only-using-the-less-than-operator-compared-to-a-trivalue-compare-functio — RedX, Dec 05 '15 at 06:40

score 4 · Accepted Answer · answered Dec 05 '15 at 06:41

4

Your compare function has a problem. It doesn't satisfy the requirements expected by std::sort. It needs to give a strict weak ordering, it must return false for equivalent elements. Try changing it to:

bool cmp(suffix a, suffix b)
{
    return (a.cur < b.cur); // note comparison is < instead of <=
}

answered Dec 05 '15 at 06:41

Blastfurnace

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It actually helps, thanks. But why do you think there is a threshold like 35? – Transcendental Dec 05 '15 at 06:43
@Enes: If you violate the algorithm's prerequisites it can lead to undefined behavior. Crashing is one possible result, the specific threshold isn't that important. – Blastfurnace Dec 05 '15 at 06:45
@Enes - FYI, if you used the Visual C++ compiler, this error would have been detected (in the debug runtime) and your program would have stopped with an assertion. The way Visual C++ checks this is to call your `cmp` function twice -- the first time with (a,b), and a second time with (b,a). If you gave an answer of `true` for both calls, the runtime asserts. The reason is that there is no way `a < b`, and at the same time `b < a`. – PaulMcKenzie Dec 05 '15 at 07:01

std::sort function gives "Bus error: 10"

1 Answers1