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Can someone explain why the sort below causes seg faults? Is this a known bug with g++ (sorting vector of pointers)? I am compiling with g++ 4.5.2. #include <iostream> #include <algorithm> #include <vector> using namespace std; typedef vector<int> A; bool face_cmp(const A *x, const A *y) { return x != y; } int main(int argc, char* argv[]) { vector<A *> vec; for (int i=0; i<100; i++) { vec.push_back( new vector<int>(i%100, i*i) ); } vector<A *>::iterator it; sort(vec.begin(), vec.end(), face_cmp); return EXIT_SUCCESS; } Compiling on codepad gives: /usr/local/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../../include/c++/4.1.2/debug/safe_iterator.h:240: error: attempt to decrement a dereferenceable (start-of-sequence) iterator. Objects involved in the operation: iterator "this" @ 0x0xbf4b0844 { type = N11__gnu_debug14_Safe_iteratorIN9__gnu_cxx17__normal_iteratorIPPN15__gnu_debug_def6vectorIiSaIiEEEN10__gnu_norm6vectorIS7_SaIS7_EEEEENS4_IS7_SB_EEEE (mutable iterator); state = dereferenceable (start-of-sequence); references sequence with type `N15__gnu_debug_def6vectorIPNS0_IiSaIiEEESaIS3_EEE' @ 0x0xbf4b0844 } Thank you for the all the quick replies. The original comp function was: if (x == y) return false; if (x->size() < y->size()) return true; else if (x->size() > y->size()) return false; else { for (register int i=0; i<x->size(); i++) { if ((*x)[i] < (*y)[i]) return true; } return false; } I just changed the first line and removed the rest. But it turns out it also suffers from not being a strict weak ordering (I forgot the case if (*x)[i] > (*y)[i]). I should probably have posted the entire function to begin with. Nevertheless, thanks again!!

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