Question

//fills my vector with pointers.
//(some are pointing places, others are set to nullptr  
vector<Tree_NodeT*> xml_trees {Build_Tree_List(program_options->Get_Files())};

//time to print them
for (auto tree = xml_trees.begin(); tree != xml_trees.end(); ++tree){
    if (*tree){
        (*tree)->Print(std::cout,4);
    }
}
//this worked! No Segfaults!

//time to print them again
for (auto tree : xml_trees){
    if (tree){
        tree->Print(std::cout,4);
    }
}
//Crash! Segfault.

Why is the second loop segfaulting, while the first loop is not?

Answer 1

EDIT:
I am a liar.
Tree_NodeT pointers were being created, but not initialized to nullptr somewhere in the Build_Tree_List function. Thus, I got a vector back where some of the pointers were pointing to valid memory, and others were just newly constructed pointers not set to null or given any address. It is still interesting that the first loop was able to handle this without crashing, while the second one segfaulted.