![](/img/trans.png)
[英]c++ error: expected constructor, destructor, or type conversion before ‘(’ token
[英]C++: Expected Constructor, Destructor or Type Conversion
试着学习C ++。 想知道是否有人可以指出我在这个错误的正确方向(双关语意图)。
该类是LinkedList(下面全部复制)。 此行发生错误:
LinkedList<T>::ListNode LinkedList::find(int pos) const {
并说:
'LinkedList'之前的预期构造函数,析构函数或类型转换
任何提示将非常感谢。
#ifndef LINKEDLIST_HPP
#define LINKEDLIST_HPP
#include <iostream>
using namespace std;
template <class T>
class LinkedList {
private:
// a ListNode consists of the item and a pointer to the next ListNode
struct ListNode {
T data;
ListNode *next;
};
int size; //Size of the list
ListNode *head; //the beginning of the list
public:
LinkedList(); // default oonstructor
~LinkedList(); // destructor
virtual bool isEmpty ();
virtual int getLength ();
virtual void insert (int pos, T item);
virtual T remove (int pos);
virtual T retrieve (int pos);
//helper methods
LinkedList(LinkedList ©List); //copy constructor
ListNode *find (int pos) const; // internal find function
};
//default constructor
template <class T>
LinkedList<T>::LinkedList() {
size = 0;
head = NULL;
}
//destructor
template <class T>
LinkedList<T>::~LinkedList() {
//loop through each node, and delete it
ListNode* current = head;
while (current != NULL) {
ListNode* next = current->next;
delete current;
current = next;
}
head = NULL; // set head node to back to null
}
//copy constructor
template <class T>
LinkedList<T>::LinkedList(LinkedList& copyList) {
size = copyList.size;
// if copyList is empty
if (copyList.head == NULL)
head = NULL;
else {
//create a new head
head = new ListNode;
head->data = copyList.head->data;
//create a new list
ListNode *newPtr = head; // start at the head
// iterate through rest of list to be copied
for (ListNode *copyPtr = copyList.head->next; copyPtr != NULL; copyPtr = copyPtr->next) {
newPtr->next = new ListNode;
newPtr->data = copyPtr->data;
}
//make last ListNode's next point to NULL
newPtr->next = NULL;
}
}
template <class T>
bool LinkedList<T>::isEmpty() {
if (size == 0)
return true;
return false;
}
template <class T>
int LinkedList<T>::getLength() {
return size;
}
// used in other methods to find a given index
template <class T>
LinkedList<T>::ListNode LinkedList::find(int pos) const {
// check that pos is in bound of LinkedList
if ((pos < 1) || pos > getLength()) {
cout << "Find position of out bounds" << endl;
return NULL;
} else { //search through ListNodes
ListNode *temp = head; // start at the head
for (int i = 1; i < pos; ++i)
temp = temp->next;
return temp;
}
}
template <class T>
T LinkedList<T>::retrieve(int pos) {
T tempData; // to hold retrieved data
try {
if ((pos < 1) || (pos > getLength())) {
cout << "Retrieve request outside LinkedList's bounds" << endl;
return NULL;
}
else { //traverse list
ListNode *temp = find(pos);
tempData = temp->data;
return tempData;
}
} catch (int e) {
cout << "Could not retrieve position " << pos << endl;
}
}
template <class T>
void LinkedList<T>::insert(int pos, T item) {
//check bounds
if ((pos < 1) || (pos > getLength() +1))
cout << "Must insert at a position between 1 and getLength() + 1" << endl;
else {
try {
//create new ListNode
ListNode *temp = new ListNode;
temp->data = item;
//if the new item is at the first position
if (pos == 1) {
temp->next = head;
head = temp;
}
else {
ListNode *prev = find(pos - 1);
temp->next = prev->next;
prev->next = temp;
}
//increment size
++size;
} catch (int e) {
cout << "Error inserting " << item << " at position " << pos << endl;
}
}
}
template <class T>
T LinkedList<T>::remove(int pos) {
//check bounds
if ((pos < 1) || (pos > getLength()))
cout << "Must remove a position between 1 and getLength()" << endl;
else {
try {
ListNode *temp; //to hold shifted node
//if node to be deleted is first node
if (pos == 1) {
temp = head;
head = head->next;
}
//for anything but the head
//write over the node before the pos'th index
else {
ListNode *prev = find(pos - 1);
temp = prev->next;
prev->next = temp->next;
}
//destroy temp, to free up memory
temp->next = NULL;
delete temp;
//decrement size
--size;
} catch (int e) {
cout << "Error removing item from position " << pos << endl;
}
}
}
#endif /* LINKEDLIST_HPP */
使用typename
限定依赖类型并添加<T>
(我不确定这是否有必要,不妨这样做):
typename LinkedList<T>::ListNode* LinkedList<T>::find(int pos) const {
请参阅: 我必须在何处以及为何要使用“模板”和“typename”关键字?
此外,您的定义不匹配。 它在类中返回一个指针,但在它之外返回一个值。
ListNode
是一个依赖类型,因此需要使用typename
进行限定。 此外,您的find
函数被声明为返回指向ListNode
的指针,但该定义按值返回ListNode
。 这似乎是一个简单的错字:
template <class T>
typename LinkedList<T>::ListNode* LinkedList<T>::find(int pos) const {
应该
LinkedList<T>::ListNode LinkedList<T>::find(int pos) const {
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.