[C++知识库]Line 30: Char 37: runtime error: member access within misaligned address 0xbebebebebebebebe for type

Line 29: Char 37: runtime error: member access within misaligned address 0xbebebebebebebebe for type ‘TreeNode’, which requires 8 byte alignment (solution.cpp)
0xbebebebebebebebe: note: pointer points here

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior prog_joined.cpp:38:37

刷题的时候遇到的，主要问题是访问空间无信息，错误代码

vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> vec_st;
        if(root==NULL) return{};
        queue<TreeNode*> st;
        st.push(root);
        //vec.push_back(root->val);
        //vec_st.push_back(vec);
        while(!st.empty()){
            //vec.clear();
            vector<int> vec;
            int len = st.size();
            for(int i=0;i<len;i--)//i--导致访问空间为null，所以出错了
            {
                TreeNode* node = st.front();
                st.pop();
                vec.push_back(node->val);//导致node为null，所以只需要改正i的值
                if(node->left) {
                    st.push(node->left);    
                }
                if(node->right){
                    st.push(node->right);
                    //vec.push_back(node->right->val);
                }
            }
            vec_st.push_back(vec);
        }
        return vec_st;
    }

修改

for(int i=0;i<len;i++)