c++ - 运行时错误。我知道在哪里，但我不知道为什么以及如何纠正它

Question

第一个问题解决后，我又遇到了另一个问题。它发生在 while 循环中

while (!infile.eof())

结果是一样的

while (getline(infile, line))

似乎不知何故它无法检查条件或其他东西，然后它再次崩溃。

[以下部分已解决]

这是函数。在插入大量 cout 以查看发生了什么之后，这

curr->prev = a->start;

是导致运行时错误的行。整个函数在这里:

busRoute readlist(const char* filename)
{
    busRoute *a;
    a = new busRoute;       //a new bus route
    stop_pointer curr;
    stop_pointer pre;
    fstream infile;
    infile.open(filename);
    string route="";
    string line="";
    int i=0;
    float df, ef;
    if (infile.is_open())
    {
        getline(infile, route);            //read route number in string
        a->routeNo=atoi(route.c_str());     //convert and store route num in int
        while (!infile.eof())
        {
            i++;
            getline(infile, line);//read text
            //generate linked list
            unsigned int pos;
            string b,c,d,e;
            pos = line.find(",");
            if (pos <100000)
            {
                b = line.substr(0,pos); //stop name
                c = line.substr(pos+1, line.length()-pos+2);
                pos = c.find(",");
                d = c.substr(0, pos);     //latitude in string
                e = c.substr(pos+1, c.length()-pos+2);    //longitude in string
                df = atof (d.c_str());    //latitude in float
                ef = atof (e.c_str());    //longitude in float
                //store b c d e into a
                if (i<2)
                {
                    a->start->stop_name= b;
                    a->start->latitude=df;
                    a->start->longitude=ef;
                    a->start->prev=NULL;
                    curr = a->start->next;

                    //sth wrong with curr->prev

                    curr->prev = a->start;
                }
                else
                {
                    curr->stop_name=b;
                    curr->latitude=df;
                    curr->longitude=ef;
                    curr->next = new stop_node;
                    pre = curr;
                    curr = curr->next;
                    curr->prev = pre;
                }
            }
        }
        infile.close();
    }
    return *a;
}

下面是.h

typedef struct stop_node* stop_pointer;

typedef struct stop_node {
  string stop_name;  // the name of the stop
  float latitude; // the latitude of the geographic coordinates of the stop
  float longitude; // the longitude of the geographic coordinates of the stop
  stop_pointer next; // the next pointer
  stop_pointer prev; // the prev pointer
};

typedef struct busRoute {
  int routeNo;  // the route number of the stop
  stop_pointer start;  // the head of the linked list
};

有人可以向我解释我犯了什么错误吗？非常感谢。

Answer 1

我第一次认为 a->start->next; 指向一些垃圾值......

所以当你尝试

curr = a->start->next;

所以在这里你给 curr 分配了垃圾值

curr->prev = a->start;

在这里您正在尝试访问导致运行时错误的无效位置。希望这会有所帮助...

///为代码工作所做的更改...

                if (i<2)
                {
                    a->start->stop_name= b;
                    a->start->latitude=df;
                    a->start->longitude=ef;
                    a->start->prev=NULL;
                   //adding 
                    a->start->next=NULL;
                    curr = a->start;

            }
            else
            {
                curr->next=new stop_node;
                curr->next->prev=curr;
                curr->stop_name=b;
                curr->latitude=df;
                curr=curr->next;
                curr->next= NULL;
            }

你的结构声明有问题...

删除这个

//typedef struct stop_node* stop_pointer;

typedef struct stop_node {
  string stop_name;  // the name of the stop
  float latitude; // the latitude of the geographic coordinates of the stop
  float longitude; // the longitude of the geographic coordinates of the stop
  stop_node *next; // the next pointer
  stop_node *prev; // the prev pointer
};


typedef struct busRoute {
  int routeNo;  // the route number of the stop
  //stop_pointer start;  // the head of the linked list
  stop_node start;       
};

如果 start 是指针类型；您需要动态分配内存然后访问内存。所以它会像这样

a->start = new bus_node();

为避免复杂化，请使用上面的 struct 和 Use 定义。运算符在其余代码中访问 start 的成员。例如。 a->start.next = NULL