记录编程错误，单链表的归并操作

错误代码如下：

#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
using namespace std;

typedef struct LNode
{
	int data;
	struct LNode* next;
}LNode;

int main()
{
	void createlist(LNode*&, int);
	void mergelist(LNode*, LNode*, LNode*&);
	void printlist(LNode*);
	LNode* a, * b, * c;
	int n1, n2;

	cout << "Please enter the length of the first linked list:";
	cin >> n1;
	createlist(a, n1);
	printlist(a);
	cout << "Please enter the length of the second linked list:";
	cin >> n2;
	createlist(b, n2);
	printlist(b);
	mergelist(a, b, c);
	printlist(c);

	return 0;
}

void createlist(LNode*& a, int n)
{
	LNode* p;

	a = (LNode*)malloc(sizeof(LNode));
	p = (LNode*)malloc(sizeof(LNode));
	a->next = p;
	cout << "Please enter the elements of the linked list one by one in an increasing order:";
	for (int i = 0; i < n; i++)
	{
		cin >> p->data; 
		if (i < n - 1) 
		{
			p->next = (LNode*)malloc(sizeof(LNode));
			p = p->next;
		}
	}
	p->next = NULL;

	return;
}

void mergelist(LNode* a, LNode* b, LNode*& c)
{
	LNode* p;

	c = (LNode*)malloc(sizeof(LNode));
	p = (LNode*)malloc(sizeof(LNode));
	c->next = p;
	while (a != NULL || b != NULL)
	{
		if (a == NULL)
		{
			p->data = b->data;
			b = b->next;
		}
		else
		{
			if (b == NULL)
			{
				p->data = a->data;
				a = a->next;
			}
			else
			{
				if (a->data < b->data)
				{
					p->data = a->data;
					a = a->next;
				}
				else
				{
					p->data = b->data;
					b = b->next;
				}
			}
		}
		if (a != NULL || b != NULL)
		{
			p->next= (LNode*)malloc(sizeof(LNode));
			p = p->next;
		}
	}
	p->next = NULL;

	return;
}

void printlist(LNode* a)
{
	a = a->next;
	while (a)
	{
		cout << a->data;
		if (a->next)
		{
			cout << " -> ";
		}

		a = a->next;
	}
	cout << endl;
	

	return;
}

运行结果及报错内容

Please enter the length of the first linked list:8
Please enter the elements of the linked list one by one in an increasing order:1 3 5 9 12 15 16 21
1 -> 3 -> 5 -> 9 -> 12 -> 15 -> 16 -> 21
Please enter the length of the second linked list:8
Please enter the elements of the linked list one by one in an increasing order:3 6 8 9 10 15 19 24
3 -> 6 -> 8 -> 9 -> 10 -> 15 -> 19 -> 24
-842150451 -> -842150451 -> 1 -> 3 -> 3 -> 5 -> 6 -> 8 -> 9 -> 9 -> 10 -> 12 -> 15 -> 15 -> 16 -> 19 -> 21 -> 24

错误原因

归并的时候忘记跳过两个待归并链表的头结点，多出来的两个结点就是它们的头结点。