为什么删除有效的堆分配指针会出现 "free(): invalid pointer" 错误？

Question

我是 C++ 的新手，正在尝试对 shared_ptr (WIP) 进行非常基本的实现。我试图在通过取消引用找到基础值后立即删除析构函数中的堆分配指针。虽然取消引用发生得很好，但删除“'ref_count'”变量会导致问题。有人可以帮忙吗？ '''

#include<iostream>

template<typename T>
class shared_ptr{
 private:
  T* native_ptr_ = nullptr;
  int* ref_count_ = nullptr;

  inline void increment_count() {
    *ref_count_++;
  }

  inline void decrement_count() {
    *ref_count_--;
  }

 public:
  shared_ptr() {
    std::cout << "shared_ptr: empty constructor" << std::endl;
    native_ptr_ = nullptr;
    ref_count_ = nullptr;
  }

  shared_ptr(T* ptr) {
    std::cout << "shared_ptr: constructor" << std::endl;
    if (ptr) {
      native_ptr_ = ptr;
      ref_count_ = new int(1);
    }
  }

  ~shared_ptr() {
    std::cout << "shared_ptr: destructor" << std::endl;
    if (ref_count_) {
      decrement_count();
      if (ref_count_ && use_count() == 0) {
        std::cout << *ref_count_ << " " << *native_ptr_ << std::endl;
        delete ref_count_;
        delete native_ptr_;
        ref_count_ = nullptr;
        native_ptr_ = nullptr;
      }
    }
  }

  int use_count() const {
    if(ref_count_) {
        return *ref_count_;
    } else {
        return 0;
    }
  }
};

int main() {
  // case1
  int* temp = new int(0);
  shared_ptr<int> a1(temp);
  return 0;
}

'''

shared_ptr: constructor
shared_ptr: destructor
0 0
free(): invalid pointer
Aborted (core dumped)

'''

Answer 1

运算符优先级给您带来了麻烦。您实际上是在递减指针，然后引用新地址。如果你提高你的警告，你会得到这样的东西：

p.cpp:35:7:   required from ‘shared_ptr<T>::~shared_ptr() [with T = int]’
p.cpp:58:26:   required from here
p.cpp:14:5: warning: value computed is not used [-Wunused-value]
   14 |     *ref_count_--;
      |     ^

您可以添加括号以在递减之前取消引用指针。

为什么删除有效的堆分配指针会出现 "free(): invalid pointer" 错误？

Why does deleting a valid heap-allocated pointer give "free(): invalid pointer" error?

c++

shared-ptr

destructor

delete-operator

reference-counting