Question

我查看了有关此问题的其他帖子，原因似乎是没有正确分配内存/解除引用。输出仅显示存储在第一个节点中的数据，该节点在Main函数中创建。但是，我使用new分配每个新节点。以下是我的代码，如果有人可以请看看：

struct people{
    Name name;
    double height;
    int weight;
};
struct Queue{
    people* ppl;
    int data;
    Queue* next;
};

void print(Queue * queueHead){
    Queue * traverse = queueHead;
    while(traverse!=NULL){
        cout << "height " << traverse->ppl->height << endl;
        traverse = traverse->next;
    }
}

void addNode(Queue*& queue, const people ppl){

    people* node = new people;
    node->name = ppl.name;
    node->height = ppl.height;
    node->weight = ppl.weight;

    Queue* traverse = queue;
    Queue* new_node = new Queue;
    while(traverse!= NULL){
        traverse= traverse->next;
    }
    new_node->ppl = node;
    new_node->next = NULL;
    traverse=new_node;
    traverse->next = NULL;
    }

int main(){
    Queue * queueHead = new Queue;

    people * node = new people;
    node->name = Ashley;
    node->height = 5.5;
    node->weight = 125;
    queueHead->ppl = node;
    queueHead->next = NULL;
    node=NULL;

people node2 = {
    .name = Peter,
    .height = 5.8,
    .weight = 145
};

people node3 = {
    .name = Bill,
    .height = 6.0,
    .weight = 160
};

people node4 = {
    .name = Mike,
    .height = 6.2,
    .weight = 150
};

people node5 = {
    .name = Chris,
    .height = 6.2,
    .weight = 140
};

addNode(queueHead,node2);
addNode(queueHead,node3);
addNode(queueHead,node4);
addNode(queueHead,node5);
//queueHead->next = NULL;

print(queueHead);

Answer 1

在addNode

Queue* traverse = queue;

是queue地址的副本，这意味着他们指向同一个地方，但这并非全部有用。作为一个例子，请注意循环迭代到列表末尾会发生什么：

while(traverse->next != NULL){
    traverse= traverse->next;
}

遍历列表，但每次都会让traverse指向NULL，并且它与列表中的任何内容分开。

traverse=new_node;

将新节点分配给traverse，但遍历是一个局部变量，仅指向与最后一个节点next相同的内容。遍历超出范围，列表未更新，新节点泄露。

但是

Queue** traverse = &queue;

让traverse始终指向next，而不仅仅是下一个的副本。如果您更新*traverse，则可以修改列表。例如，

void addNode(Queue*& queue, const people ppl){ 
 // I think you dropped a & here const pass by value isn't all that useful.

    people* node = new people;
    node->name = ppl.name;
    node->height = ppl.height;
    node->weight = ppl.weight;
    // the above should be done in a people copy constructor

    Queue** traverse = &queue;
    Queue* new_node = new Queue;
    while((*traverse)!= NULL){
        traverse= &(*traverse)->next; //traverse points at next instead of
                                      // being a copy.
    }
    new_node->ppl = node;
    new_node->next = NULL;
    *traverse=new_node; // pointing what traverse points at at the new node 
    (*traverse)->next = NULL; // this should really be done in a Queue constructor
}

Answer 2

您的添加节点功能实际上从未将新节点添加到现有队列中。

试试这个

void addNode(Queue*& queue, const people ppl){

    people* node = new people;
    node->name = ppl.name;
    node->height = ppl.height;
    node->weight = ppl.weight;

    Queue* traverse = queue;
    Queue* new_node = new Queue;

    while(traverse->next != NULL){
        traverse= traverse->next;
    }
    new_node->ppl = node;
    new_node->next = NULL;
    traverse->next = new_node;
}

继续获得node2到node5的“无法访问地址0x0的内存”

2 个答案: