实现状态机时面临double free

Question

对于一项任务，我计划在 C++ 中实现一个状态机。 我试图保留一个提供以下内容的上下文对象：

1. 用于跟踪当前状态的 state_ 对象
2. 一个 TransitionTo() 方法来促进转换到新状态。

   当我编写示例实现并对其进行测试时，我遇到了 double free 错误。

   我需要社区的帮助来指导我了解可能出现的问题。 非常感谢。

   
   #include <iostream>
   #include <string>
   
   class State;
   
   /* Context class and method implementation */
   class Context
   {
       State* state_;
   public:
       explicit Context(State* state);
       void TransitionTo(State* newState);
   };
   
   Context::Context (State* state): state_ (nullptr) 
   {
       this->TransitionTo(state);
   }
   
   void Context::TransitionTo(State* newState)
   {
       std::cout <<"Requesting state transition to " << newState->stateName<<"\n";
       std::string previous_state_name = "None";
       if (this->state_ != nullptr)
       {
           previous_state_name = this->state_->stateName;
           delete this->state_;
       }
       this->state_ = newState;
       std::cout << "State changed from "<< previous_state_name << " to "<< this->state_->stateName << "\n";
       this->state_->set_context(this);
   }
   
   
   
   /* State class and method implementation */
   class State
   {
       protected:
           Context* context_;
       public:
           std::string stateName;
           void set_context(Context* newContext);
           virtual ~State();
           
   };
   
   State::~State()
   {
       std::cout << stateName <<" state deleted \n";
       delete context_ ;
   }
   
   void State::set_context(Context *newContext) 
   {
       this->context_ = newContext;
   }
   
   
   /* Declaring different states which are derived from State */
   class HappyState : public State
   {
   public:
       HappyState();
   };
   
   HappyState::HappyState()
   {
       stateName = "Happy";
   }
   
   class NeutralState : public State
   {
   public:
       NeutralState();
   };
   
   NeutralState::NeutralState()
   {
       stateName = "Neutral";
   }
   
   class SadState : public State
   {
   public:
       SadState();
   };
   
   SadState::SadState()
   {
       stateName = "Sad";
   }
   
   /* Test the implementation */
   int main()
   {
       Context* ctx  = new Context(( new NeutralState()));
       
       ctx->TransitionTo(new HappyState());
       
       ctx->TransitionTo(new SadState());
   
       return 0;
   }
   

   当我运行这段代码时，我得到以下输出： Output snapshot

Answer 1

我发现了这个错误，这确实是一个非常愚蠢的错误。

我正在删除 ~State() 中的 context_ ，这删除了我的原始上下文。