Several important functional operations of general two-way circular list

Creation of doubly circular linked list

struct DNode{struct DNode* prev; //point to the previous nodestruct DNode* next; //point to the next nodechar elem[]; // use a flexible array to accept any type};

Insert before the node, insert after the node and delete the node in the doubly circular linked list

//Insert before nodevoid insert_before(struct DNode* node, const void* pElem, size_t elemSize){assert(node!=NULL && pelem!=NULL && elemsize!=0);//Because a flexible array is used, the size of the inserted data must be added to allocate memorystruct DNode* insNode = (struct DNode*)malloc(sizeof(struct DNode) + elemSize);if(insNode == NULL)return;insNode->next = node;insNode->prev = node->prev;memcpy(node->elem, pElem, elemSize); //Because we don't know the type of elem, we use memory copynode->prev->next = insNode; //The order of these two sentences cannot be chaoticnode->prev = insNode;}//Insert after node, there is not much difference from the above, just change a few wordsvoid insert_after(struct DNode* node, const void* pElem, size_t elemSize){assert(node!=NULL && pelem!=NULL && elemsize!=0);//Because a flexible array is used, the size of the inserted data must be added to allocate memorystruct DNode* insNode = (struct DNode*)malloc(sizeof(struct DNode) + elemSize);if(insNode == NULL)return;insNode->next = node->next;insNode->prev = node;memcpy(node->elem, pElem, elemSize);node->next->prev = insNode; //The order of these two sentences cannot be disorderednode->next = insNode;}// delete nodevoid delete_dnode(struct DNode* node){assert(node ​​!= NULL);if(node->next = node) //If node is the head node, why can't it be deletedreturn;node->prev->next = node->next;node->next->prev = node->prev;free(node);}//create a header nodestruct DNode* create_cdlist(void){//Because the head node does not store data, you can directly allocate the memory of the size of the structurestruct DNode* list = (struct DNode*)malloc(sizeof(struct DNode));if(list != NULL) //If the creation fails, return NULL directly{list->next = list;list->prev = list; //There is no data at the beginning and it is a ring, so it points to itself first}return list;}//Get the posth node, pos starts from 1struct DNode* get_dnode(struct DNode* list, size_t pos){assert(list != NULL);struct DNode* node = list->next;size_t i;for(i = 1; inext);if(i < pos) //When pos is greater than the total length of the linked list, node has already looped and exited the loop and pointed to the head node,// this time return emptyreturn NULL;return node;}