c-是什么导致了双链表中append Node函数的分段错误

Question

我的双链表实现如下，每个节点都有一个由四个值组成的数组

#define EMPTYNODE 0
struct node {
short data[4]; // pay attention
struct node* next;
struct node* prev;
};
typedef struct node nodeQ_t;
typedef enum{
LIST_FALSE = 0,
LIST_TRUE = 1,
} status_t;
nodeQ_t* createNode(short values[4]){
nodeQ_t* node = (nodeQ_t*)malloc(sizeof(node));
for(int i=0; i < 4; i++){
node->data[i] = values[i];
}
node->next = EMPTYNODE;
node->prev = EMPTYNODE;
return node;
}

现在，我正试图以一种方式编写append函数，即为其提供head和createNode函数中创建的节点，以便将其附加到列表中。。。。但它造成了分割错误。。。

status_t appendNode(nodeQ_t* head, nodeQ_t* newNode){
if(head == EMPTYNODE || newNode == EMPTYNODE){
return LIST_FALSE;
};
nodeQ_t* currentNode = head;
while(currentNode != EMPTYNODE){
if(currentNode->next == EMPTYNODE){ //it means that current node is tail
currentNode->next = newNode;  //segmenttion fault arises at exactly this line 
newNode->prev = currentNode;
}
currentNode = currentNode->next;
}
return LIST_TRUE;
}

请告诉我是什么原因。。。供您参考，我的主要功能是

int main(){
short array[4] = {1,2,3,4};
nodeQ_t* head  = createNode(array);
printList(head);

short array2[4] = {5,6,7,8};
nodeQ_t* newNode = createNode(array2);
appendNode(head, newNode);

printList(head);

return 0;
}

如果你需要任何进一步的信息或解释，请告诉我

Answer 1

如注释中所述，一旦到达终点，您需要break退出循环：

while(currentNode != EMPTYNODE) {
if (currentNode->next == EMPTYNODE) {
currentNode->next = newNode;
newNode->prev = currentNode;
// need a break here
}
currentNode = currentNode->next;
// When at the end of the list the 1st time through, 
// currentNode is the newly created node because you have
//     currentNode->next = newNode
// then
//     currentNode = currentNode->next
// On the next iteration, the new node next ends up getting pointed to itself 
// since on that iteration newNode and currentNode are the same.
// and you end up with an infinite loop.
}

另一种选择是在currentNode->next:上循环

while (currentNode->next) {
currentNode = currentNode->next;
}
currentNode->next = newNode;
newNode->prev = currentNode;

我应该注意，这是有效的，因为您之前已经确保currentNode不是NULL。

此外，您在这里的分配是错误的：

nodeQ_t* node = (nodeQ_t*)malloc(sizeof(node));

因为node是指针，而sizeof(node)是指针的大小，而不是struct node的大小。应该是

nodeQ_t* node = (nodeQ_t*)malloc(sizeof(*node));

Answer 2

你最终会陷入无尽的循环：

while(currentNode != EMPTYNODE){
if(currentNode->next == EMPTYNODE){ //it means that current node is tail
currentNode->next = newNode;  //segmenttion fault arises at exactly this line 
newNode->prev = currentNode;
}

CCD_ 8将总是不同于CCD_ 9。添加新元素后添加中断或返回：

while(currentNode != EMPTYNODE){
if(currentNode->next == EMPTYNODE){ //it means that current node is tail
currentNode->next = newNode;  //segmenttion fault arises at exactly this line 
newNode->prev = currentNode;
return LIST_TRUE;
}