Question

The problem is to find periodic graph patterns in a dataset. So I have 1000 timesteps with a graph(encoded as integers) in each timestep. So, there are 999 possible periods in which the graph can occur. Also I define a phase offset defined as (timestep mod period). For a graph which was first seen in the 5th timestep with period 2, the phase offset is 1.

I am trying to create a bidimensional array of lists in C++. Each cell contains a list containing graphs having a specified period and phase offset. I keep inserting graphs in the corresponding lists.

list<ListNode> A[timesteps][phase offsets]

ListNode is a class with 4 integer variables.

This gives me Segmentation fault. Using 500 for the size runs fine. Is this due to lack of memory or some other issue?

Thanks.

Answer 1

Sounds like you’re running out of stack space. Try allocating it on the heap, e.g. through std::vector, and wrap in try ... catch to see out of memory errors instead of crashing.

(Edit: Don’t use std::array since it also allocates on the stack.)

try {
   std::vector<std::list<ListNode> > a(1000000);   // create 1000*1000 lists
   // index a by e.g. [index1 * 1000 + index2]
   a[42 * 1000 + 18].size(); // size of that list

   // or if you really want double subscripting without a wrapper function:
   std::vector<std::vector<std::list<ListNode> > > a(1000);
   for (size_t i = 0; i < 1000; ++i) {   // do 1000 times:
       a[i].resize(1000);                // default-create and create 1000 in each
   }
   a[42][18].size(); // size of that list

} catch (std::exception const& e) {
    std::cerr << "Caught " << typeid(e).name() << ": " << e.what() << std::endl;
}