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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. class Machine
  5. {
  6.    class State *current;
  7.    class State *nextstate; 
  8.    void check_transition(); 
  9. public:
  10.     Machine();
  11.     void setCurrent(State *s)
  12.     {
  13.     	nextstate = s; 
  14.         //current = s;
  15.     }
  16.     void set_on();
  17.     void set_off();
  18. };
  19.  
  20. class State
  21. {
  22.   public:
  23.     virtual void set_on(Machine *m)
  24.     {
  25.         cout << "   already ON\n";
  26.     }
  27.     virtual void set_off(Machine *m)
  28.     {
  29.         cout << "   already OFF\n";
  30.     }
  31.     virtual ~State(){}
  32. };
  33.  
  34. void Machine::check_transition() { 
  35.    	   if (nextstate) {
  36.    	   	   swap (current, nextstate);
  37.    	   	   delete nextstate;  // this contains the former current  
  38.    	   	   nextstate = nullptr; 
  39.    	   }
  40.    }
  41.  
  42. void Machine::set_on()
  43. {
  44.    current->set_on(this);
  45.    check_transition(); 
  46. }
  47.  
  48. void Machine::set_off()
  49. {
  50.   current->set_off(this);
  51.   check_transition(); 
  52. }
  53.  
  54. class ON: public State
  55. {
  56.   public:
  57.     ON()
  58.     {
  59.         cout << "   ON-ctor ";
  60.     };
  61.     ~ON()
  62.     {
  63.         cout << "   dtor-ON\n";
  64.     };
  65.     void set_off(Machine *m);
  66. };
  67.  
  68. class OFF: public State
  69. {
  70.   public:
  71.     OFF()
  72.     {
  73.         cout << "   OFF-ctor ";
  74.     };
  75.     ~OFF()
  76.     {
  77.         cout << "   dtor-OFF\n";
  78.     };
  79.     void set_on(Machine *m)
  80.     {
  81.         cout << "   going from OFF to ON";
  82.         m->setCurrent(new ON());
  83.     }
  84. };
  85.  
  86. void ON::set_off(Machine *m)
  87. {
  88.   cout << "   going from ON to OFF";
  89.   m->setCurrent(new OFF());
  90. }
  91.  
  92. Machine::Machine() 
  93. {
  94. 	nextstate = nullptr; 
  95.     current = new OFF();
  96.     cout << '\n';
  97. }
  98.  
  99. int main()
  100. {
  101.   void(Machine:: *ptrs[])() = 
  102.   {
  103.     &Machine::set_off, &Machine::set_on
  104.   };
  105.   Machine fsm;
  106.   int num;
  107.   cout << "Enter 0/1: ";
  108.  
  109.   while (cin >> num)
  110.   {
  111.  
  112.     (fsm.*ptrs[num])();
  113.    cout << "Enter 0/1: ";
  114.   }
  115. }
Success #stdin #stdout 0s 3236KB
comments (?)
stdin 
1 1 0
stdout 
   OFF-ctor 
Enter 0/1:    going from OFF to ON   ON-ctor    dtor-OFF
Enter 0/1:    already ON
Enter 0/1:    going from ON to OFF   OFF-ctor    dtor-ON
Enter 0/1:
https://ideone.com/tfPFRm
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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