附加在C ++中的链接列表中不起作用

Question

This is my class

class NumberList
{
private:
   // Declare a structure for the list
   struct ListNode
   {
      double value[10];           // The value in this node
      struct ListNode *next;  // To point to the next node
   }; 

   ListNode *head;            // List head pointer

public:
   // Constructor
   NumberList()
      { head = nullptr; }

   // Destructor
   ~NumberList();

   // Linked list operations
   void appendNode(double []);
   void insertNode(double []);
   void deleteNode(double []);
   void displayList() const;
};

This is my append function and I can't get it to work -- i keep getting an error message.

void NumberList::appendNode(double num[])
{
   ListNode *newNode;  // To point to a new node
   ListNode *nodePtr;  // To move through the list

   // Allocate a new node and store num there.
   newNode = new ListNode;
   newNode->value = num;
   newNode->next = nullptr;

   // If there are no nodes in the list
   // make newNode the first node.
   if (!head)
      head = newNode;
   else  // Otherwise, insert newNode at end.
   {
      // Initialize nodePtr to head of list.
      nodePtr = head;

      // Find the last node in the list.
      while (nodePtr->next)
         nodePtr = nodePtr->next;

      // Insert newNode as the last node.
      nodePtr->next = newNode;
   }
}

Error message:

prog.cpp: In member function ‘void NumberList::appendNode(double*)’: prog.cpp:40:19: error: incompatible types in assignment of ‘double*’ to ‘double [10]’ newNode->value = num;

Any suggestions about what i'm doing wrong?

Answer 1

The type of the parameter num in void NumberList::appendNode(double num[]) is really a pointer (= double* ), rather than an array with a defined number of elements.

Using std::array<double,10> in your structure and as the parameter to appendNode would be a good solution.

This:

struct ListNode
{
  double value[10];
...

Becomes:

struct ListNode
{
  std::array<double,10> value;
...

And your function parameters would be declared as:

void appendNode(const std::array<double,10>& num);

newNode->value = num; requires no change.