EXC_BAD_ACCESS 在 unordered_map

Question

代码是c++14中的简单Trie实现。执行add("name")函数时弹出如下错误：EXC_BAD_ACCESS (code=1, address=0x20))

下面是一些调试图片：

遵循以下代码：

struct TrieNode {
  string value;
  unordered_map<char, TrieNode *> children = {};
};

class Trie {
 public:
  TrieNode *root = new TrieNode;

  TrieNode *find(string query);

  int countPartialFind(string query);

  void add(string value);

 private:
  void add(string value, TrieNode *node);

  TrieNode *createNewNode(string &value, int counter, unordered_map<char, TrieNode *> &children);

  void add(string value, int counter, TrieNode *node);

  TrieNode *findNode(char query, unordered_map<char, TrieNode *> &children);
};

TrieNode *Trie::find(string value) {
  TrieNode *tmpNode = root;
  for (int counter = 0; counter < value.length(); counter++) {
    tmpNode = findNode(value[counter], tmpNode->children);
    if (tmpNode == NULL) {
      return NULL;
    }
  }

  return tmpNode;
}

int Trie::countPartialFind(string query) {
  TrieNode *matchNode = find(query);
  if (matchNode == NULL) {
    return 0;
  }

  return matchNode->children.size();
}

void Trie::add(string value, int counter, TrieNode *node) {
  for (; counter < value.length(); counter++) {
    node = findNode(value[counter], node->children);
    if (node == NULL) {
      node = createNewNode(value, counter, node->children);;
    }
  }
}

TrieNode *Trie::findNode(char query, unordered_map<char, TrieNode *> &children) {
  unordered_map<char, TrieNode *>::const_iterator search = children.find(query);
  if (search == children.end()) {
    return NULL;
  }
  return search->second;
}

TrieNode *Trie::createNewNode(string &value, int counter, unordered_map<char, TrieNode *> &children) {
  TrieNode *newNode = new TrieNode;
  newNode->value = value.substr(0, counter + 1);
  char tmp = value[counter];
  children[tmp] = newNode;
  return newNode;
}

void Trie::add(string value) {
  if (value.length() == 0) { return; }
  int counter = 0;

  TrieNode *tmpNode = findNode(value[counter], root->children);

  if (tmpNode == NULL) {
    tmpNode = createNewNode(value, counter, root->children);
  }

  add(value, ++counter, tmpNode);
}

这个问题应该是微不足道的，但我听不懂。感谢您的帮助，如果还有任何其他优化或代码设计可以完成，请告诉我。

Answer 1

在3参数Trie::add函数中，调用createNewNode时，node已知为NULL。第三个参数 node->children 取消引用 NULL 指针，导致未定义的行为，在这种情况下会导致崩溃。

如果您在局部变量的值处查找调用堆栈，您会看到这一点。

EXC_BAD_ACCESS 在 unordered_map

EXC_BAD_ACCESS in unordered_map

c++

unordered-map