I am working on my final project for CS class, C++, and I cannot for the life of me figure out this problem. The project is about implementing a Trie, but I don’t think that’s relevant. I think the root of all this lies in memory management. In the template code given

// Trie.h
...
class Trie
{
public:
    struct Node
    {
        std::vector<Trie::Node*> next{}; // point of interest
        ~Node(); 
        void insert(std::string s); 
        const Node* traverse(std::string s) const; 
        bool lookup(std::string s) const; 
        size_t get_completions(std::vector<std::string>& completions, 
                               size_t limit) const; 
    }* _root;
...
}
...

when I call _root->next.size() from the Trie constructor, I get 18446726657961603453. I don’t know if this number has any significance.

Whatever, I resize it in the constructor even though it should have been initialized as empty, then I go to work on a function that implements part of the Trie.

// Trie.cpp
...
void Trie::Node::insert(string s)
{
    std::vector<Trie::Node*>* level = &next;
    for(char c : s){
        if((*level).size() <= static_cast<size_t>(c)){
            (*level).resize(static_cast<int>(c)+1); // Where it breaks, I included the rest so you have an idea of what the code is doing but its not relevant. 
        }       
        if(!(*level)[c]){
            (*level)[c] = new Trie::Node;
            (*level)[c]->next.resize(0);
        } 
        level = &(((*level)[c])->next);
    }
    if((*level).size() == 1){
        (*level).resize(1);
    }
    (*level)[0] = new Trie::Node;
    
}
...

I didn’t expect it to break, at least with segfaults and all that. The line of code that breaks works fine if I set it to 0. For resizes of 1-5, the debugger leads me to this line of code with a segfault.

::new((void*)__p) _Tp(std::forward<_Args>(__args)...);

For values greater than that, I get this and the debugger aborts because an error occurred.

_GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n));

To add, this also appears in the terminal

“double free or corruption (out)

make: *** [Makefile:29: run_main] Aborted (core dumped)”

I’m truly stumped as to what is happening, any clues?

I will also note, I know that (*level) can be replaced with level->. I don’t know why I ended up writing it like this.