Question

我正在编写双向链接列表，一切都很顺利但是当我在结构中读取字符串值时遇到崩溃（代码行在函数中被注释＆＃34; struct Node * GetNewNode（）＆＃ 34）：

        #include <iostream>
        #include <String>
        #include <fstream>
        #include <cstdlib>

        using namespace std;

        struct Node {
            int sv;
            double real;
            bool log;
            char simb;
            string str;
            struct Node* next;
            struct Node* prev;
        };

        struct Node* head; // global variable - pointer to head node.
        //----------------------------
        struct Node* GetNewNode();
        void Initialize(Node *stack);
        void InsertAtTail(Node *stack);
        void Print(Node *stack);
        //----------------------------
        //Creates a new Node and returns pointer to it.

        ifstream fd("duom.txt");
        struct Node* GetNewNode() {
            struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
            fd >> newNode->sv;
            fd >> newNode->real;
            string loginis;
            fd >> loginis;
            if (loginis == "TRUE")
                newNode->log = true;
            else
                newNode->log = false;
            fd >> newNode->simb;
            //fd >> newNode->str;           //uncommented code in this row crashes the program
            newNode->prev = NULL;
            newNode->next = NULL;
            return newNode;
        }

        //Inserts a Node at head of doubly linked list
        void Initialize(Node *stack) {
            stack = head;
        }

        //Inserts a Node at tail of Doubly linked list
        void InsertAtTail(Node *stack) {
            struct Node* temp = stack;
            struct Node* newNode = GetNewNode();
            if(head == NULL) {
                head = newNode;
                return;
            }
            while(temp->next != NULL)
                temp = temp->next; // Go To last Node
            temp->next = newNode;
            newNode->prev = temp;
        }

        //Prints all elements in linked list in reverse traversal order.
        void Print(Node *stack) {
            struct Node* temp = stack;
            if(temp == NULL)
                return; // empty list, exit
            // Going to last Node
            while(temp->next != NULL)
                temp = temp->next;
            // Traversing backward using prev pointer
            while(temp != NULL) {
                cout << temp->sv << " ";
                cout << temp->real << " ";
                if (temp->log == true)
                    cout << "TRUE " << " ";
                else
                    cout << "FALSE " << " ";
                cout << temp->simb << " ";
                //cout << temp->str << "\n";
                temp = temp->prev;
            }
            printf("\n");
        }

        int main() {

            /*Driver code to test the implementation*/
            head = NULL; // empty list. set head as NULL.
            // Calling an Insert and printing list both in forward as well as reverse direction.
            Initialize(head);
            InsertAtTail(head);
            Print(head);
            InsertAtTail(head);
            Print(head);
            fd.close();
        }

输入数据是：
4 5.27 TRUE $ asdf
6 7.3 TRUE＃qwer
9 8.8 FALSE @ zxvc
7 6.35否！ vbmn
1 0.89 TRUE％ghjk

有人可以解释这里有什么问题吗？

Answer 1

而不是使用C标准函数malloc

      struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));

你必须使用operator new

在这种情况下，编译器将调用类std::string的构造函数来创建数据成员str

函数std::string只是分配一个请求大小的原始内存。它对类的构造函数一无所知。

Answer 2

malloc分配原始内存块。这对于仅存储数据的简单（POD）数据类型就足够了。但是std::string需要调用其构造函数才能正确初始化。因此，您必须使用new分配节点：

Node* newNode = new Node();

通常，在C ++中很少需要malloc（它不会调用任何构造函数）。它是一个C函数。

请注意，您需要拨打delete而不是free来释放由new分配的内存。

程序崩溃是因为字符串？

2 个答案: