我是第一次使用指针，想写一个删除节点的函数和一个删除节点的函数。我的代码可以识别我插入的键和数据（例如：键=123，数据=123）。然而，当我尝试删除键123时，它却不能识别它的存在。这是我的LList.cpp，如果需要的话，我可以加入其他代码。
#include <iostream>
#include "LList.h"
//----------------------------------------------------
// constructor & destructor
//----------------------------------------------------
LList::LList() {
head = NULL;
} // constructor (default)
LList::~LList() {
if (head) delete head;
} // destructor
//----------------------------------------------------
// print
//----------------------------------------------------
// prints each node in the list, or EMPTY when there
// are no nodes to print
//----------------------------------------------------
void LList::print() {
if (head == NULL)
cout << "EMPTY\n\n";
else {
node* p;
p = head;
while (p != NULL) {
p->print();
p = p->next;
}
cout << endl;
}
} // print()
//----------------------------------------------------
// search
//----------------------------------------------------
// Given: key to search for
// Returns: pointer to a node in the list found to have
// the given search key, or NULL for not found
//----------------------------------------------------
node* LList::search(int srchKey) {
if (head == NULL)
return NULL;
node* itr = head;
while (itr != NULL) {
if (itr->key == srchKey)
itr = itr->next;
}
return itr;
} // search()
//----------------------------------------------------
// findNode
//----------------------------------------------------
// Given: a key to search for
// Searches for a node with the given key, and if
// found, invokes the print() method in the found node.
// Otherwise, prints "not found"
//----------------------------------------------------
void LList::findNode(int srchkey) {
if (head == NULL) {
cout << "not found\n";
}
node* itr = head;
while (itr != NULL) {
if (itr->key == srchkey) {
print();
}
itr = itr->next;
}
cout << "not found\n";
} // findNode()
//----------------------------------------------------
// getb4
//----------------------------------------------------
// Given: a pointer to a node in the list
// Returns: a pointer to the node in the list BEFORE
// the one pointed to by r, OR
// NULL when r is the head or not found in
// the list
//----------------------------------------------------
node* LList::getb4(node* r) {
node* tmp = head;
while (tmp->next != NULL) {
if (tmp->next == r)
return tmp;
tmp = tmp->next;
}
return NULL;
} // getb4()
//----------------------------------------------------
// insert
//----------------------------------------------------
// Given: key and data for a new node
// Allocates/populates a new node
// When a node with the same key already exists:
// the current/old node is replaced by the new one
// and the old one is placed on the new one's
// duplicate list.
// Otherwise, the new node is prepended to the head
// of the list.
//----------------------------------------------------
void LList::insert(int k, string d) {
node* newNode = new node();
node* currentNode, *prevNode;
newNode->key = k;
newNode->data = d;
if (head == NULL) {
head = newNode;
}
else {
currentNode = search(k);
if (currentNode == NULL) {
newNode->next = head;
head = newNode;
}
if (currentNode == head) {
newNode->next = head->next;
head->next = NULL;
newNode->dup = head;
head = newNode;
}
prevNode = getb4(currentNode);
if (prevNode == NULL)
return;
prevNode->next = newNode;
//newNode->next = currentNode->next;
currentNode->next = NULL;
newNode->dup = currentNode;
}
} // insert()
//----------------------------------------------------
// remove
//----------------------------------------------------
// Given: a pointer to a node in the list to be removed
// BUT NOT DELETED/DESTROYED
// Returns: TRUE - when the node was successfully removed
// FALSE - when the given node is NULL or the node
// is not actually in the list.
// Simply removes the node from the linked list.
// (including setting the NEXT pointer in the node to NULL)
//----------------------------------------------------
bool LList::remove(node* r) {
if (r == NULL || search(r->key) == NULL) {
return false;
}
if (r == head) {
head = head->next;
}
else {
node* prev = getb4(r);
prev->next = r->next;
}
r->next = NULL;
return true;
} // remove()
//----------------------------------------------------
// drop
//----------------------------------------------------
// Given: key of a node to drop
// Returns: TRUE when a node was found and deleted
// FALSE when a node with the given key not found,
// or the remove() fails.
// Searches for a node in the list with the given key:
// When found, removes and deletes the node
//----------------------------------------------------
bool LList::drop(int k) {
node* currentNode = search(k);
if (currentNode == NULL || !remove(currentNode))
return false;
node* tmp = currentNode;
while (tmp != NULL) {
currentNode = currentNode->dup;
remove(tmp);
tmp = currentNode;
}
return true;
} // drop()
//----------------------------------------------------
// max
//----------------------------------------------------
// Returns: a pointer to the node with the highest key
// or NULL when there list is empty.
node* LList::max() {
if (head == NULL)
return NULL;
node* max = head;
node* tmp = head->next;
while (tmp != NULL) {
if ((tmp->key) > (max->key)) {
max = tmp;
}
tmp = tmp->next;
}
return max;
} // max()
这个循环。
while (itr != NULL) {
if (itr->key == srchKey)
itr = itr->next;
}
return itr;
是不正确的。你要么是在找到键的情况下进行迭代，要么根本没有迭代。你需要在列表中迭代。和 搜索键，同时这样做。
while (itr != NULL) {
if (itr->key == srchKey)
break;
itr = itr->next;
}
return itr;
还有，你的析构器是不正确的；你只删除了第一个节点，而泄露了其余的节点。你需要通过迭代linked-list来删除所有节点。
LList::~LList() {
while (head)
delete std::exchange(head, head->next);
}
还有，最好使用 nullptr而不是 NULL.