为什么将“ char”分配给“ char”会产生段错误？ C ++

Question

I have a class that looks like this:

class myTreeNode
{
     public:   
        char Data;
        myTreeNode *childA = NULL;   //A's always go in child1
        myTreeNode *childT = NULL;   //T's always go in child2
        myTreeNode *childC = NULL;   //c's always go in child3
        myTreeNode *childG = NULL;   //G's always go in child4
};

However, when I go to assign Data a value, I receive a seg fault. I do this like:

root->childT->Data = p_data;

Where p_data is a char = t and root is a pointer created by myTreeNode *root = new myTreeNode; . Why when going to assign Data a value would I get a seg fault? Isn't it just the same as doing char Data = 't' ?

Answer 1

Your children are not pointing to any memory location. You have only created a new instance for the root node. You are getting a segfault because you are dereferencing a null pointer.

For example:

class myTreeNode
{
public:
  char Data;
  myTreeNode *childA = NULL;   //A's always go in child1
  myTreeNode *childT = NULL;   //T's always go in child2
  myTreeNode *childC = NULL;   //c's always go in child3
  myTreeNode *childG = NULL;   //G's always go in child4
};

int main()
{
  // allocate memory
  myTreeNode *root = new myTreeNode;
  root->childT = new myTreeNode; // allocate child

  root->childT->Data = 'a';

  // delete allocated memory
  delete root->childT;
  delete root;
  return 0;
}