#include<stdio.h>
#include<stdlib.h>
typedef struct NODE{
    struct NODE *bwd;
    struct NODE *fwd;
    int value;
}NODE;

insert(NODE *rootp,int value)
{
    NODE *thisnode;
    NODE *nextnode;
    NODE *newnode;

    for(thisnode=rootp;(nextnode=thisnode->fwd) !=NULL;thisnode=nextnode)
    {
        if(nextnode->value==value)
            return 0;
        else
        if(nextnode->value > value)
            break;
    }

    newnode = (NODE*)malloc(sizeof(NODE));
    if(newnode == NULL)
        return -1;
    newnode->value=value;
   
    newnode->fwd=nextnode;
    thisnode->fwd = newnode;
    if(thisnode!=rootp)
    {
        newnode->bwd = thisnode;
    }
    else
    {
        newnode->bwd =NULL;
    }
    if(nextnode!=NULL)
        nextnode->bwd = newnode;
    else
        rootp->bwd = newnode;
    return 1;
}

void main()
{
    NODE *s1;
    NODE *s2;
    NODE *s3;
    NODE *root;
    root=(NODE*)malloc(sizeof(NODE));
    s1=(NODE*)malloc(sizeof(NODE));
    s2=(NODE*)malloc(sizeof(NODE));
    s3=(NODE*)malloc(sizeof(NODE));
   
    s1->value=5;
    s2->value=12;
    s3->value=15;
   
    root->fwd=s1;
    s1->bwd=NULL;
    s1->fwd=s2;
    s2->bwd=s1;
    s3->fwd=NULL;
    root->bwd=s3;

    insert(root,3);
    printf("%d\n",root->fwd->value);
    printf("%d\n",root->fwd->fwd->value);
    printf("%d\n",root->fwd->fwd->fwd->value);
    printf("%d\n",root->fwd->fwd->fwd->fwd->value);
}
运行后就会出错 打印出3 5 12   这是怎么回事？？