链表冒泡排序逻辑错误

Question

下面我用C编写了一个简单的链表程序，它保存了一个点及其到原点的距离。我的问题是，当调用排序函数时，它不能正确排序。我花了相当多的时间调试gdb，但运气不好。我对C和处理指针比较陌生，所以如果有人能帮助我，我会非常感激!

我本来打算发布一个输出的图像，但是我似乎没有足够的声誉，所以输出看起来像下面这样:

点:(3,1)-距离:3.16228

点:(4,1)-距离:4.12311

点:(1,1)-距离:1.41421

点:(7,1)-距离:7.07107

test.c文件:

#include <stdlib.h>
#include <stdio.h>
#include "point.h"
typedef struct node
{
    Point p;
    double distance;
    struct node *next;
} node;
void insertAtFront(node **start, Point *ip);
void sort(node *start);
void swap(node *a, node *b);
void printList(node *start);
int main(int argc, char **argv)
{
    Point *insertPoint = malloc(sizeof(Point));
    node *head = NULL;
    point_set(insertPoint,7.0,1.0);
    insertAtFront(&head,insertPoint);
    point_set(insertPoint,1.0,1.0);
    insertAtFront(&head,insertPoint);
    point_set(insertPoint,4.0,1.0);
    insertAtFront(&head,insertPoint);
    point_set(insertPoint,3.0,1.0);
    insertAtFront(&head,insertPoint);
    sort(head);
    printList(head);
}
void insertAtFront(node **start, Point *ip)
{
    node *node1 = (node*)malloc(sizeof(node));
    node1->p = *ip;
    node1->next = *start;
    *start = node1;
}
void sort(node *start)
{
    Point *tp1 = malloc(sizeof(Point));
    Point *tp2 = malloc(sizeof(Point));
    int swapped;
    node *node1;
    node *node2 = NULL; 
    node *tempNode; 
    double d1;
    double d2;
    if(start == NULL)
        return;
    do
    {
        swapped = 0;
        node1 = start;
        *tp1 = node1->p;        
        tempNode = node1->next;     
        *tp2 = tempNode->p;     
        d1 = distanceFromOrigin(tp1);
        d2 = distanceFromOrigin(tp2);
        while(node1->next != node2)
        {
            if(d1 > d2)
            {
                swap(node1,node1->next);
                swapped = 1;
            }
            node1 = node1->next;
        }
        node2 = node1;
    }
    while(swapped);
}
void swap(node *a, node *b)
{
    Point *tp;
    *tp = a->p;
    a->p = b->p;
    b->p = *tp;
}
void printList(node *start)
{
    node *temp = start;
    Point *tp = malloc(sizeof(Point));
    printf("n");
    while(temp != NULL)
    {
        *tp = temp->p;
        printf("Point: (%g,%g) - Distance: %gn", point_getX(tp), point_getY(tp), distanceFromOrigin(tp));
        temp = temp->next;
    }
}

point.c文件:

#include <stdio.h>
#include "point.h"
#include <math.h>
void point_translate(Point *p, double x, double y)
{
    point_set(p,(point_getX(p)+x),(point_getY(p)+y));
}
double point_distance(const Point *p1, const Point *p2)
{
    double temp1 = (point_getX(p1) - point_getX(p2));
    double temp2 = (point_getY(p1) - point_getY(p2));
    double temp3 = (temp1*temp1)+(temp2*temp2);
    double dist = sqrt(temp3);
    return dist;
}
double distanceFromOrigin(const Point *p1)
{
    double x = point_getX(p1);
    double y = point_getY(p1);
    double temp = (x*x)+(y*y);
    double dist = sqrt(temp);
    return dist;
}

point.h文件:

#ifndef _POINT_H_
#define _POINT_H_
typedef struct Point 
{
  double x;
  double y;
} Point;
void point_translate(Point *p, double x, double y);
double point_distance(const Point *p1, const Point *p2);
double distanceFromOrigin(const Point *p1);
static inline double point_getX(const Point *p)
{
  return p->x;
}
static inline double point_getY(const Point *p)
{
  return p->y;
}
static inline Point *point_set(Point *p, double x, double y)
{
  p->x = x; 
  p->y = y;
  return p;
}
#endif

Answer 1

swap函数中的局部变量tp没有初始化。你的编译器应该就此警告你。然后你就可以访问它了这是未定义行为。

Answer 2

当与node1->next交换node1时，您需要更改指向node1的前一个节点的next指针，或者您可以在node1和node1->next之间交换数据，使next指针保持不变。

如果你要交换指针，下面是交换之前的样子:

node0->next = node1, node1->next = node2, node2->next = node3

和swap后:

node0->next = node2, node2->next = node1, node1->next = node3

这只适用于相邻节点。如果节点不是相邻的，那么在swap之前:

nodea->next = node1, node1->next = nodeb
nodec->next = node2, node2->next = noded

交换后

nodea->next = node2, node2->next = nodeb
nodec->next = node1, node1->next = noded