C language structure linked list node insertion method (before and after)

封装一个函数 Implements the ability to insert new nodes from the specified node（You can choose from before or after）
函数原型如下：

struct Test* insertNode(struct Test *p,struct Test *new,int data,char* way) 

The first parameter is the address of the head node of the original linked list
The second parameter is the new node address to insert
The third parameter is the position of the node to insert,Represented by the value of the structure（The actual item can be freely changed）
The fourth parameter is the insertion method（前：AHEAD / 后:BEHIND）

The idea of ​​inserting nodes after the introduction is introduced:
一：Insert before：
1.If it is inserted before the head node,Then directly make the next node of the new node equal to the head node,Then go back to the new node
2.如果不是头节点,In the process of traversing the linked list, the current node is judgedP的下一个节点P->NEXTWhether the value of is the position to insert,如果是：
第一步：Then the new nodeNEXT等于P->NEXT
第二步：P的NEXT指向新节点.

代码如下：

struct Test* insertNodeAhead(struct Test *p,struct Test *new,int data)//Insert the node from before
{
    
	struct Test *head=p;
	if(head->data==data)//Insert before the first
	{
    
		new->next=head;
		return new;
	}
	
	while(p->next!=NULL)
	{
    
		if(p->next->data==data)
		{
    
			new->next=p->next;
			p->next=new;
			return head;
		}
		p=p->next;
	}
	printf("no this data:%d\n",data);
	return head;
}

二：Insert from behind：
Inserting from the back is simpler,Just judge one situation：
Determine the current node in the process of traversing the linked listPWhether the value of is the position to insert,如果是：
第一步：Then the new nodeNEXT等于P->NEXT
第二步：P的NEXT指向新节点.

代码如下：

struct Test* insertNodeBehind(struct Test *p,struct Test *new,int data)//Insert nodes from the back
{
    
	struct Test* head=p;
	while(p!=NULL)
	{
    
		if(p->data==data)
		{
    
			new->next=p->next;
			p->next=new;
			return head;
		}
		p=p->next;
	}
	printf("no this data:%d\n",data);
	return head;
}

整体代码实现如下：

#include<stdio.h>
#include<string.h>

#define AHEAD "ahead"
#define BEHIND "behind"

struct Test
{
    
	int data;
	struct Test *next;
};

void printLink(struct Test *p)
{
    
	while(p!=NULL)
	{
    
		printf("%d\n",p->data);
		p=p->next;
	}
}
struct Test* insertNodeBehind(struct Test *p,struct Test *new,int data)//Insert nodes from the back
{
    
	struct Test* head=p;
	while(p!=NULL)
	{
    
		if(p->data==data)
		{
    
			new->next=p->next;
			p->next=new;
			return head;
		}
		p=p->next;
	}
	printf("no this data:%d\n",data);
	return head;
}

struct Test* insertNodeAhead(struct Test *p,struct Test *new,int data)//Insert the node from before
{
    
	struct Test *head=p;
	if(head->data==data)//Insert before the first
	{
    
		new->next=head;
		return new;
	}
	
	while(p->next!=NULL)
	{
    
		if(p->next->data==data)
		{
    
			new->next=p->next;
			p->next=new;
			return head;
		}
		p=p->next;
	}
	printf("no this data:%d\n",data);
	return head;
}

struct Test* insertNode(struct Test *p,struct Test *new,int data,char* way) 
{
    
	struct Test *head=p;
	int ret=-1;
	
	if(strstr(way,"behind")!=NULL)
	{
    
		ret=1;
	}
	else if(strstr(way,"ahead")!=NULL)
	{
    
		ret=0;
	}
	
	switch(ret)
	{
    
		case 1:
			head=insertNodeBehind(head,new,data);
			break;
		case 0:
			head=insertNodeAhead(head,new,data);
			break;
		default:
			printf("Parm error\n");
			return NULL;
	}
	return head;
}


int main()
{
    
	struct Test t1={
    1,NULL};
	struct Test t2={
    2,NULL};
	struct Test t3={
    3,NULL};
	struct Test t4={
    4,NULL};
	struct Test t5={
    5,NULL};
	
	struct Test new1={
    8,NULL};
	struct Test new2={
    0,NULL};
	struct Test new3={
    100,NULL};

	struct Test *head=&t1;
	
	t1.next=&t2;
	t2.next=&t3;
	t3.next=&t4;
	t4.next=&t5;
	
	printLink(head);
	
	head=insertNode(head,&new1,3,BEHIND);
	head=insertNode(head,&new2,5,AHEAD);
	head=insertNode(head,&new3,1,AHEAD);
	printf("after insert:\n");
	printLink(head);

}

运行结果如下：