Why can't I check to see if a char stored in a pointer and a char are equivalent?

Question

I have a program that returns an error after I've compiled it in g++, then run it in a Unix environment. The error is that my program says 'Segmentation error' before it can do anything. This error is occurring when I try to set a new nodes data pointer equal to something. I know this because when I test this code in Visual Studio when I try to check if(curr->data == ch); with curr being a pointer, data being the char element that the list is made up of, and ch being the char passed into the bool LinkedList::find(char ch) function, Visual Studio breaks (stops) at that line of code. For context, here's part of my header file (with if(curr->data == ch); towards the end):

#include <ostream>

class LinkedList
{
public:
        LinkedList();
        ~LinkedList();

        bool find(char ch);
private:
    struct node
    {
            node();
            char data;
            node * next;
    };
    node * head;
    node * curr;
    node * prev;
};
LinkedList::LinkedList() : head(nullptr), curr(nullptr), prev(nullptr);
LinkedList::node::node() : data('\0'), next(nullptr);
LinkedList::~LinkedList()
{
    if (!head) // head is null and so list is empty
    {
            return; //nothing to delete
    }

    for(curr = head; head; /* head isn't NULL*/ delete curr /*delete first element*/)
    {
            curr = head;  // set curr to head of list
            head = curr->next;  // move head over to next element (or make it null)
    }
}
bool LinkedList::find(char ch)
{
        if(head)
        {
                for(curr = head; curr && curr->data != ch; curr = curr->next);
                if(curr->data == ch)
                {
                        //std::cout << "'" << ch << "' is in the list." << std::endl;
                        return true;
                }
                else
                {
                        //std::cout << "'" << ch << "' isn't in the list." << std::endl;
                        return false;
                }
                //std::cout << "The list is empty" << std::endl;
                return false;
        }
        else
        {
                //std::cout << "The list is empty" << std::endl;
                return false;
        }
}

I wish I could give you guys more context, but I have no idea how to fix this. I thought a char and a pointer to a char were the same type; after all, Visual Studio doesn't break when the for loop checks: curr->data != ch;.

Answer 1

for(curr = head; curr && curr->data != ch; curr = curr->next);

has two exit conditions. One is you find a node with ch. The other is curr == NULL. The next line after the loop exits

if(curr->data == ch)

tests the data member of a curr that might be NULL. Tears in rain... Time to die....

In order to test data, the program first has to find and read it. Finding it is easy, it is at most a few bytes at best after memory address 0, but reading it is problematic. Your program does not own address 0 and cannot read it, triggering an access violation.

By convention, the first chunk of memory is reserved and invalid to make trapping invalid accesses like this one easy. Rather than returning a garbage answer and appearing to function, the program typically crashes. But it might not if convention is not followed.