在 std::__cxx11::basic_string 中獲取未知的分段錯誤“（地址） <char, std::char_traits<char> ,..., std::allocator<char> &gt; 常量&amp;) 常量()

Question

我正在用 C++ 編寫一個程序，它代表一個具有這些類和結構的論壇：

struct Date{            /* struct used to get a random day for each comment */
    int d,m,y,h,min;
    Date();
    void GetDate() const;
};

class Post{
  private:
    std::string Title;
    std::string Creator;
    std::string text;
    Date PostDate;
    int id;
  public:
    Post();
    ~Post();
    void postprint() const;
    int idprint();
    std::string get_creator() const; //returns the creator of the post
};

class Thread{
  private:
    std::string Subject;
    std::string Creator;
    Date ThreadDate;
    int post_nums = rand()%10+1;   // this will be the number of posts that will be made in the thread, used in threadprint()
    Post *posts = new Post[post_nums]; //so the randomizer doesn't return 0 array cells, max 10 posts for each thread
  public:
    Thread();
    ~Thread();
    std::string subjprint() const;
    void threadprint() const;
    int getnums() const; //returns the number of posts in the posts array
    Post *getposts() const; //returns to a pointer the array of posts
};

class Forum{
  private:
    std::string Title;
    Thread *threads = new Thread[3];
    //void printt(int) const;
  public:
    Forum(const std::string);
    ~Forum();
    void Print_threads() const;
    void Print_specified_thread(const std::string);
    Thread *Find_thread_subject(const std::string);
    void Print_specified_post(const int);
    Post *Find_specified_post(const int);
};

struct Post_list{
  Post *post;
  Post_list *next;
  Post_list *prev;
};

struct Tree_node{
  std::string Creator;
  Post_list *list_ptr;
  Tree_node *left;
  Tree_node *right;
};

class Thread_tree{
  private:
    Tree_node *node_root;
    void Tree_create(Tree_node *);
    int Tree_empty(Tree_node *);
    void Tree_sort(const Thread *, Tree_node *);
    void Tree_insert(const std::string, Tree_node *);
  public:
    Thread_tree(const Thread *);
};

現在我試圖將每個線程的評論的創建者放入一個 BST 中，將它們整理出來，其中每個節點struct Tree_node都有一個創建者字符串和他在列表中的評論。 class Thread_tree構造class Thread_tree是這樣的

Thread_tree::Thread_tree(const Thread *Thread1){  //constructor only to be called once
  cout << "Creating tree of post creators from thread " << Thread1->subjprint() << endl;
  Tree_create(this->node_root); //points root to NULL
  Tree_sort(Thread1, this->node_root);
}

而Tree_sort()是

void Thread_tree::Tree_sort(const Thread *Thread1, Tree_node *root){
  int k = Thread1->getnums(); //k is assigned to the number of the posts that the thread has
  Post *post_ptr = Thread1->getposts(); //ptr is assigned to the posts array of the thread
  for (int i=0; i<k; i++){
    cout << "\ni is " << i << endl;
    Tree_insert((post_ptr+i)->get_creator(), root);
  }
}

和Tree_insert()

void Thread_tree::Tree_insert(const string creator, Tree_node *root){
  if (Tree_empty(root)){
    root = new Tree_node;
    root->Creator = creator;
    root->list_ptr = NULL;
    root->left = NULL;
    root->right = NULL;
  }
  else if (creator.compare(root->Creator) < 0){ //creator in string1 is smaller than the root->Creator
        Tree_insert(creator, (root->left));    // in ascending order

      }
   if (creator.compare(root->Creator) > 0) {//creator in string1 is bigger than the root->Creator
        Tree_insert(creator, (root->right));   //in ascending order
      }
}

在 main() 中，當我制作一棵樹Thread_tree Tree1(thread); 由於“線程”是指向現有線程的指針，因此出現分段錯誤。 我運行 gdb 調試器，並在使用bt后收到此消息：

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7b7625a in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::compare(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) const ()
   from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
(gdb) bt
#0  0x00007ffff7b7625a in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::compare(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) const ()
   from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#1  0x00000000004025f1 in Thread_tree::Tree_insert (this=0x7fffffffe7c0, creator="user1234", root=0x1002) at classes.cpp:211
#2  0x00000000004026be in Thread_tree::Tree_insert (this=0x7fffffffe7c0, creator="user1234", root=0x604110) at classes.cpp:218
#3  0x00000000004024e4 in Thread_tree::Tree_sort (this=0x7fffffffe7c0, Thread1=0x616d98, root=0x604110) at classes.cpp:197
#4  0x00000000004023b7 in Thread_tree::Thread_tree (this=0x7fffffffe7c0, Thread1=0x616d98) at classes.cpp:181
#5  0x0000000000402f03 in main () at main.cpp:19

我不明白問題是什么，從我從消息中了解到的，程序在Tree_insert()的第二次調用時Tree_insert()

Answer 1

你的問題是Tree_create(this->node_root);

Tree_create創建傳遞給它的指針的副本並將NULL分配給該副本，而this->node_root保持不變並且在Tree_sort時未初始化。

最簡單的解決方案是將NULL （或nullptr ，在c++11更可取）直接分配給this->node_root

這同樣適用於您的其他方法。 當您按值傳遞指針時，對它的任何賦值都是在復制時完成的。 這里的解決方案是通過引用傳遞指針（例如Tree_create(Tree_node*& root) ）