一、从指定节点后方插入

插入逻辑如图：

插入前：A指向B，B指向C

插入后：B为插入点，当要插入D时就要让B指向D，D再指向C（插入前B的指向）

#include <stdio.h>

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

void printLink(struct Test *head)
{
	while(1){
		if(head != NULL){
		printf("%d ",head->data);
		head = head->next;
		}else{
			printf("\n");
			break; 
		}
	}
}

int getLinkNum(struct Test *head)
{
	int cnt =0;
	while(head !=NULL){
		cnt ++;
		head = head->next;
	}
	return cnt;
}

int searchLink(struct Test *head,int data)
{
	while(head != NULL){
		if(head->data == data){
			return 1;
		}
		head = head->next;
	}
	return 0;
}

int insertBhind(struct Test *head,int data,struct Test *new)
{
	struct Test *p = head;        
	while(p !=NULL){
		if(p->data == data){
			new->next = p->next;    //新插入的链表指向插入点的链表
			p->next = new;          //插入点指向新插入的链表
			return 1;    
		}
		p = p->next;                //循环结束，p指向后面的链表
	}
	return 0;
}
int main(){
	struct Test t1 = {1,NULL};
	struct Test t2 = {2,NULL};
	struct Test t3 = {3,NULL};
	struct Test t4 = {4,NULL};
	
	t1.next = &t2;
	t2.next = &t3;
	t3.next = &t4;
	
	printLink(&t1);
	int ret =getLinkNum(&t1);
	printf("total num = %d\n",ret);
	
	ret = searchLink(&t1,1);
	if(ret = 0){
		printf("没有data = 1\n");
	}else{
		printf("有data = 1\n");
	}
	
	struct Test new={100,NULL};      //定义“new”链表
	insertBhind(&t1,3,&new);        //在数据等于3的位置插入“new”链表
	printLink(&t1);
	return 0;
}

二、从指定节点前方插入