c++ - 遇到段错误 : It looks like my comparator is trying to compare nodes out of scope

Question

我遇到了段错误。我相信这与我进行比较的方式有关。我对 C++ 感到难过和陌生。

最后一行 pq.pop() 是进入堆栈跟踪并导致失败的调用。执行 ./a.out 时没有打印出任何东西

class Node {
    public:

    Node() {}

    Node(int b) {
        bound = b;
    }

    Node(int b, Node * p) {
        bound = b;
        parent = p;
    }

    void addChild(Node& n) {
        n.parent = this;    
    }

    Node * parent;

    int bound;
};



class CompareNode {

public:
    bool operator()(Node *n, Node *o)
    {
        cout << "Comparing " << n->bound;
        cout << " to " << o-> bound <<endl;
        return n->bound > o->bound; 
    }
};

---

在主目录下

---

std::priority_queue<Node*, vector<Node*>, CompareNode> pq;
Node* root = new Node();
Node* node;
for(int i = 0; i < n; i++) {
  node = new Node(matrix[0][i], root);
  pq.push(node);
}

pq.pop();

---

GDB

---

(gdb) run
Program received signal SIGSEGV, Segmentation fault.
0x00000000004027e7 in void std::__pop_heap<__gnu_cxx::__normal_iterator<Node**, std::vector<Node*, std::allocator<Node*> > >, CompareNode>(__gnu_cxx::__normal_iterator<Node**, std::vector<Node*, std::allocator<Node*> > >, __gnu_cxx::__normal_iterator<Node**, std::vector<Node*, std::allocator<Node*> > >, __gnu_cxx::__normal_iterator<Node**, std::vector<Node*, std::allocator<Node*> > >, CompareNode) ()
(gdb) backtrace
#0  0x00000000004027e7 in void std::__pop_heap<__gnu_cxx::__normal_iterator<Node**, std::vector<Node*, std::allocator<Node*> > >, CompareNode>(__gnu_cxx::__normal_iterator<Node**, std::vector<Node*, std::allocator<Node*> > >, __gnu_cxx::__normal_iterator<Node**, std::vector<Node*, std::allocator<Node*> > >, __gnu_cxx::__normal_iterator<Node**, std::vector<Node*, std::allocator<Node*> > >, CompareNode) ()
#1  0x0000000000401e13 in void std::pop_heap<__gnu_cxx::__normal_iterator<Node**, std::vector<Node*, std::allocator<Node*> > >, CompareNode>(__gnu_cxx::__normal_iterator<Node**, std::vector<Node*, std::allocator<Node*> > >, __gnu_cxx::__normal_iterator<Node**, std::vector<Node*, std::allocator<Node*> > >, CompareNode)
    ()
#2  0x0000000000401a11 in std::priority_queue<Node*, std::vector<Node*, std::allocator<Node*> >, CompareNode>::pop() ()
#3  0x00000000004015dc in main ()

Answer 1

C++ 并不经常为您检查必要的先决条件。如果在空结构上调用 pop，结果很可能是崩溃。所以这是我首先要看的地方。

您可以使用 -D_GLIBCXX_DEBUG 在 GCC 中获取此检查。它添加了边界检查、迭代器验证等，在任何情况下都是一套很好的训练轮。