Question

I’m not entirely sure why I’m getting a segfault for this piece of code. I have an array of object pointers I want to create. Here is my code.

   edge **test = new edge*[a]; //Edge is a predefined class I have created. a is a my size of my array.
   graphCreate2(test, vertices, roads, a); //Note roads is an edge class I have already created also

However, when I try to access edge ** test’s elements, I get a segfault. Here’s how I accessed it.

void graphCreate2(edge **test, int vertices, edge *roads, int a)
{
  for(int i = 0; i < a; i++)
  {
    e[i]->setEdgeSrc(roads[i].getEdgeSrc());
    e[i]->setEdgeDes(roads[i].getEdgeDes());
    e[i]->setLength(roads[i].getLength());
    cout << e[i]->getLength() << " " << e[i]->getEdgeSrc() << " " << endl;
  }
}

Might anyone know why I’m getting this segfault? I thought I allocated memory to it as the constructor is called when creating the array Thanks!

Answer 1

The constructor is not called for each edge. You’re only creating the array of pointers, but they point to garbage.

You need to create them all in a loop.

void graphCreate2(edge **test, int vertices, edge *roads, int a)
{
  for(int i = 0; i < a; i++)
  {
    test[i] = new edge();  // create the edge
    test[i]->setEdgeSrc(roads[i].getEdgeSrc());
    test[i]->setEdgeDes(roads[i].getEdgeDes());
    test[i]->setLength(roads[i].getLength());
    cout << test[i]->getLength() << " " << test[i]->getEdgeSrc() << " " << endl;
  }
}