Memory leak in linked list class - c++

Question

If I run this in visual studio it tells me there are memory leaks, but I don't see anything wrong with my destructor. What did I do wrong? Is it because the memory leak function is being called before the destructor? Am I not supposed to call the memory leak function at the end?
I already posted this on codereview and they said it work fine, but I hadn't included a destructor then. I added one now but I'm not sure if it's actually working.
#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
#include <iostream>
using std::cout;
using std::cin;
using std::endl;
struct node {
int key;
struct node *next;
};
class linked_list {
private:
struct node *head;
struct node *tail;
public:
linked_list() {
head = nullptr;
tail = nullptr;
}
void create(int key) {
struct node *temp;
temp = new struct node;
temp->key = key;
temp->next = nullptr;
head = temp;
tail = head;
}
void insert(int key) {
if (key < head->key) {
insert_beginning(key);
}
else if ((head->next == nullptr) || (key > tail->key)) {
insert_end(key);
}
else {
insert_middle(key);
}
}
void insert_beginning(int key) {
if (head->next == nullptr) {
tail = head;
}
struct node *temp;
temp = new struct node;
temp->key = key;
temp->next = head;
head = temp;
}
void insert_end(int key) {
struct node *temp;
temp = new struct node;
temp->key = key;
temp->next = nullptr;
if (head->next == nullptr) {
head->next = temp;
tail = temp;
}
else {
tail->next = temp;
}
tail = temp;
}
void insert_middle(int key) {
struct node *temp;
temp = new struct node;
temp->key = key;
struct node *current = head;
struct node *prev = current;
while (current->key < temp->key) {
prev = current;
current = current->next;
}
prev->next = temp;
temp->next = current;
}
void delete_node(int key) {
if (head == nullptr) {
cout << "List is empty\n";
return;
}
if (head->key == key) {
if (head->next == nullptr) {
delete(head);
head = tail = nullptr;
}
struct node *temp = head;
head = head->next;
delete(temp);
}
else {
struct node *current = head;
struct node *prev = current;
while ((current->key != key) && (current->next != nullptr)) {
prev = current;
current = current->next;
}
if ((current->key != key) && (current->next == nullptr)) {
cout << "Key not found\n";
}
else if ((current->key == key) && (current->next == nullptr)) {
tail = prev;
prev->next = nullptr;
delete(current);
}
else {
prev->next = current->next;
delete(current);
}
}
}
void search_node(int key) {
if (head->key == key || tail->key == key) {
cout << "Node found\n";
return;
}
struct node *current = head;
while ((current->key != key) && (current->next != nullptr)) {
current = current->next;
}
if (current->key == key) {
cout << "Node found\n";
}
else {
cout << "Node not found\n";
}
}
void print_nodes(void) {
struct node *current = head;
while (current != nullptr) {
cout << current->key << '\n';
current = current->next;
}
}
~linked_list() {
struct node *current = head;
struct node *prev = current;
while (current->next != nullptr) {
current = current->next;
delete(prev);
prev = current;
}
delete(prev);
}
};
int main(void) {
linked_list list;
list.create(0);
for (int i = 1; i < 20; ++i) {
list.insert(i);
}
list.search_node(5);
list.search_node(0);
list.search_node(-1);
list.delete_node(19);
list.delete_node(0);
list.print_nodes();
_CrtDumpMemoryLeaks();
}

Answer 1

When you call _CrtDumpMemoryLeaks();, you have not yet destructed your list object.
UPDATE
Adding a set of braces so as to destruct list before doing the memory leak diagnostic.
int main(void) {
{
linked_list list;
list.create(0);
for (int i = 1; i < 20; ++i) {
list.insert(i);
}
list.search_node(5);
list.search_node(0);
list.search_node(-1);
list.delete_node(19);
list.delete_node(0);
list.print_nodes();
}
_CrtDumpMemoryLeaks();
}

Answer 2

The usual way to do a leak check as late as possible with MSVC is to enable the automatic dump functionality, with the following code:
_CrtSetDbgFlag(_CrtSetDbgFlag(_CRTDBG_REPORT_FLAG)|_CRTDBG_LEAK_CHECK_DF);
This will do a leak check after main/WinMain has returned and global object destructors have run. And if you've ever seen an MFC dump report that is how it is enabled.