~vector() causes SIGSEGV when exit - c++

Question

Thats the Store Credit problem on Google code jam.
https://code.google.com/codejam/contest/351101/dashboard#s=p0
My code gives out a SIGSEGV after running the large test. But the answer is correct!
#include <cstdio>
#include <algorithm>
#include <vector>
using namespace std;
int ps[1000]={0};
vector<int> indice[1000];
int main() {
int cases; scanf("%d", &cases);
for(int j=1;j<=cases;j++) {
printf("Case #%d: ", j);
int c, is; scanf("%d%d", &c, &is);
for(int i=0;i<=c;i++) ps[i]=0;
for(int i=0;i<=c;i++) indice[i].clear();
for (int i = 0; i < is; i++) {
int it; scanf("%d", &it);
indice[it].push_back(i+1);
ps[it]=1;
if (c-it>0&&ps[c-it]) {
int a, b;
a = indice[it][0];
b = indice[c-it][0];
if(c==2*it&&indice[it].size()>1) {
b=indice[it][1];
}
if (a!=b) {
printf("%d %d\n", min(a,b),max(a,b));
}
}
}
}
return 0;
}
So I use valgrind to find out what's going on .. but it seems that it's not my problem.
==17599== Invalid free() / delete / delete[] / realloc()
==17599== at 0x4C2A4BC: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==17599== by 0x401669: __gnu_cxx::new_allocator<int>::deallocate(int*, unsigned long) (new_allocator.h:98)
==17599== by 0x4013CD: std::_Vector_base<int, std::allocator<int> >::_M_deallocate(int*, unsigned long) (stl_vector.h:156)
==17599== by 0x400F60: std::_Vector_base<int, std::allocator<int> >::~_Vector_base() (stl_vector.h:142)
==17599== by 0x400D8D: std::vector<int, std::allocator<int> >::~vector() (stl_vector.h:351)
==17599== by 0x400C48: __tcf_0 (a.cpp:6)
==17599== by 0x5383900: __run_exit_handlers (exit.c:78)
==17599== by 0x5383984: exit (exit.c:100)
==17599== by 0x5369773: (below main) (libc-start.c:258)
==17599== Address 0x1 is not stack'd, malloc'd or (recently) free'd
==17599==
==17599==
==17599== HEAP SUMMARY:
==17599== in use at exit: 128 bytes in 1 blocks
==17599== total heap usage: 4,527 allocs, 4,527 frees, 113,664 bytes allocated
==17599==
==17599== LEAK SUMMARY:
==17599== definitely lost: 0 bytes in 0 blocks
==17599== indirectly lost: 0 bytes in 0 blocks
==17599== possibly lost: 0 bytes in 0 blocks
==17599== still reachable: 128 bytes in 1 blocks
==17599== suppressed: 0 bytes in 0 blocks
==17599== Rerun with --leak-check=full to see details of leaked memory
==17599==
==17599== For counts of detected and suppressed errors, rerun with: -v
==17599== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 2 from 2)
I'm so confused... Could anybody tell me what's going on? I'm a newbie of C++ ..
Thank you very much.

Answer 1

As I understand valgrind, it can't detect that you are writing outside of the bounds of arrays that are staticly allocated. So let's allocate them on the heap.
vector<int> *indice = new vector<int>[1000];
int *ps = new int[1000];
Then, you will see errors come out of valgrind. Including:
==7168== Invalid read of size 8
==7168== at 0x4008D6: main (stl_vector.h:735)
==7168== Address 0x4c39e10 is 8 bytes after a block of size 24,008 alloc'd
==7168== at 0x4A07152: operator new[](unsigned long) (vg_replace_malloc.c:363)
==7168== by 0x400791: global constructors keyed to indice (foo.cc:6)
==7168== by 0x400C35: ??? (in /tmp/foo)
==7168== by 0x4005F2: ??? (in /tmp/foo)
==7168==
==7168== Invalid read of size 8
==7168== at 0x4008DA: main (stl_vector.h:735)
==7168== Address 0x4c39e18 is 16 bytes after a block of size 24,008 alloc'd
==7168== at 0x4A07152: operator new[](unsigned long) (vg_replace_malloc.c:363)
==7168== by 0x400791: global constructors keyed to indice (foo.cc:6)
==7168== by 0x400C35: ??? (in /tmp/foo)
==7168== by 0x4005F2: ??? (in /tmp/foo)
==7168==
And using gdb, I can see that the SIGSEGV occurs when you access indice[1433], which is outside of the bounds of indice.
I also imagine that your actual issue is that for the large dataset, the variables bounds are listed as:
N = 50
3 ≤ I ≤ 2000
Are you sure you shouldn't be allocating 2001 elements, instead of 1000?