c++ - 段错误(核心已转储)- 访问冲突读取位置 x

Question

我正在编写一个有点像玩具的程序来进入 C++。但是，我在代码中非常特定的一行遇到段错误时遇到了很多麻烦。我知道段错误意味着我试图访问未提供给我程序的内存。代码(有点)如下(实际上只是复制粘贴太大了):

class car {
protected:
   int speed;
   std::string brand;
public:
   car (int s, std::string b):speed(s),brand(b) {
       std::cout << "New car has been created" << endl;
   }
   virtual int is_stopped () {
      if (speed==0) return 1;
      else return 0;
   }
   virtual void speed_up () {
       speed++;
   }
   car* clone () {
      car* tmp(this);
      return tmp;
   }
};
class fast_car : public car {
public:
   fast_car (int s, std::string b):car(s,b) { } 
};
class slow_car : public car {
public:
   slow_car (int s, std::string b):car(s,b) { }
};
class highway {
   int number_of_cars;
   car **first;           //There are derived classes from car hence the                double pointer
public:
   highway (int c, int s, std::string b):number_of_cars(c) {
      first = new car*[c];
      for (int i=0;i<c/2;i++)
          first[i] = new fast_car (s,b);
      for (int i=c/2;i<c;i++)
          first[i] = new slow_car (s,b);
   }
   void speed_up () {
      int pos;
      pos = rand()%number_of_cars;    //give me a random number between 0 and number_of_cars;
      if (pos!=0) pos--;   //We don't want position -1
          first[pos]->speed_up ();
      clone_fast (first[pos], (number_of_cars - pos - 1)); //the second argument is the remaining array "spots" until the end of the array
   }



   void clone_fast (car* cur, int rem) {
      car* tmp;
      for (int i=-;i<=rem;i++) 
         if ((cur+1)->is_stopped ()) {   //Exact line where I get the segmentation fault
            tmp = cur->clone ();
            cur++;
         }
   }
};

原来如此。我试图为您提供一切可能来重现该问题。我会尝试解决任何进一步的问题。任何帮助将不胜感激。

Answer 1

car* 由 new 创建，不一定连续；它们当然不是您可以使用指针算术的数组。 (car*) + 1 与 (car**)[i + 1] 不同(后者更像是 (car**) + 1 )。您可能想要更像 (*(first + 1))->doThing() 的东西，而不是 (first[X] + 1)->doThing() .

编辑:更清楚一点，如果你不能做 car[X + 1]，那么你就不能做 *(car + 1)。由于 clone_fast() 中的 car 是对象指针而不是数组，您不能执行 car[X + 1]，因此 (cur + 1)->is_stopped() 是错误的。