Question

我打算写一个简单的SDL应用程序，所以我想我应该实现一个简单的链表，我可以稍后再扩展。现在经过一番努力，我决定在这里寻求帮助。

我知道链表，我读到了它。我看到了几个实现，不是那么难，很容易掌握。所以我想我应该能够自己实现一个。我猜我在这里严重忽略了一些东西。：（

首先这段代码编译不好，分段错误。其次，我不认为如果我能够克服我在指针中所做的基本错误，它会产生我想要的东西。

你能告诉我我的代码中的错误吗？我哪里做错了？

这是一个用于编辑的liveworkspace链接 http://liveworkspace.org/code/1qu1RN $ 1

以下是我在Cygwin gcc上遇到的错误

temp [v 0] -> 0.460241 0.000000 0.050356
temp [v 1] -> 0.072079 0.153807 0.864573
temp [v 2] -> 0.683917 0.709301 0.080479
temp [v 3] -> 0.295755 0.264795 0.894696
address of ptemp @ 1629101750

[v 0] -> linked vertex is  7731159828445146316135105405324534341657178000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.000000 578395405356271.125000 1310047834864691498231654014730274851713450000.000000
Segmentation fault (core dumped)

这是代码

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define NEWline printf("\n")

typedef struct position {
    double x;
    double y;
    double z;
} position;

struct datalist {
    position v;
    struct datalist  *pnext;

};
typedef struct datalist datalist;

void initializeList (datalist *head);
void addList_II (datalist *head , double data[3] );

void initializeList (datalist *head){
    position pv= {0,0,0};
    head = (datalist *) malloc ( sizeof (head) );
        if (head == NULL){ printf("cannot allocate memory");  exit(1); }
    head->v=pv;
    head->pnext=NULL;
}

void addList_II ( datalist *head , double data[3] ) {

    datalist *adddata;
    adddata = (datalist *)malloc ( sizeof (datalist) );
        if (adddata == NULL) { printf("cannot allocate memory for insertion data"); exit(1); }
    adddata->v.x = data[0];
    adddata->v.y = data[1];
    adddata->v.z = data[2];

    adddata->pnext = head->pnext;
    head=adddata;
}

int main() {

    datalist *ptemp;
    datalist temp;
    int i,c; //counters
    datalist *head;

    initializeList(head);

    for ( i = 0; i < 4; i++ ) {
        double t[3];
        srand ( time ( NULL )*i+234 );
            temp.v.x = ((double ) rand()  )/ RAND_MAX;
        srand ( time ( NULL )*i*546 );
            temp.v.y = ((double ) rand()  )/ RAND_MAX;
        srand ( time ( NULL )*i*567+345 );
            temp.v.z = ((double ) rand()  )/ RAND_MAX;
        t[0] = temp.v.x; t[1] = temp.v.y; t[2] = temp.v.z;

        printf ( "temp [v %d] -> %F %F %F \n",i, temp.v.x, temp.v.y, temp.v.z );
        addList_II (head, t );
    }

    c=0;
    ptemp=head;
    while (ptemp!=NULL) {
        printf("[v %d] -> linked vertex is  %F %F %F \n", c, ptemp->v.x,ptemp->v.y, ptemp->v.z);
        ptemp=ptemp->pnext;

    }
}

Answer 1

在你的addList_II中，你设置了错误的指针。您正在接收新节点并将其下一个指针指向头部的下一个指针，该指针为空。

   void addList_II ( datalist *head , double data[3] ) {
        datalist *adddata;
        adddata = (datalist *)malloc ( sizeof (datalist) );
            if (adddata == NULL) { printf("cannot allocate memory for insertion data"); exit(1); }
        adddata->v.x = data[0];
        adddata->v.y = data[1];
        adddata->v.z = data[2];

        //    adddata->pnext = head->pnext; //not THIS
        adddata->pnext = head;        //DO THIS
        head=adddata;
    }

此外，您的指针超出了函数调用的范围。你需要做的是传入**变量。这意味着你传入指向指针的指针，指针指向你的内存块。您可以通过取消兑换本地*来修改原始指针，并在返回时表现良好。

如果您需要更多解释，请询问，但这是解决方案

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define NEWline printf("\n")

typedef struct position {
    double x;
    double y;
    double z;
} position;

struct datalist {
    position v;
    struct datalist  *pnext;

};
typedef struct datalist datalist;

void initializeList (datalist **head);
void addList_II (datalist **head , double data[3] );

void initializeList (datalist **head){
    position pv= {0,0,0};
    *head = (datalist *) malloc ( sizeof (datalist) );
        if (head == NULL){ printf("cannot allocate memory");  exit(1); }
    (*head)->v=pv;
    (*head)->pnext=NULL;
}

void addList_II ( datalist **head , double data[3] ) {
    datalist *adddata;
    adddata = (datalist *)malloc ( sizeof (datalist) );
        if (adddata == NULL) { printf("cannot allocate memory for insertion data"); exit(1); }
    adddata->v.x = data[0];
    adddata->v.y = data[1];
    adddata->v.z = data[2];

    adddata->pnext = *head;        //DO THIS
    *head=adddata;
}

int main() {

    datalist *ptemp;
    datalist temp;
    int i,c; //counters
    datalist *head;

    initializeList(&head);


    for ( i = 0; i < 3; i++ ) {
        double t[3];
        srand ( time ( NULL )*i+234 );
            temp.v.x = ((double ) rand()  )/ RAND_MAX;
        srand ( time ( NULL )*i*546 );
            temp.v.y = ((double ) rand()  )/ RAND_MAX;
        srand ( time ( NULL )*i*567+345 );
            temp.v.z = ((double ) rand()  )/ RAND_MAX;
        t[0] = temp.v.x; t[1] = temp.v.y; t[2] = temp.v.z;

        printf ( "temp [v %d] -> %F %F %F \n",i, temp.v.x, temp.v.y, temp.v.z );
        addList_II (&head, t );
    }

    ptemp=head;

    while (ptemp!=NULL) {
       NEWline; 
        printf("[v ] -> linked vertex is  %F %F %F \n", ptemp->v.x,ptemp->v.y, ptemp->v.z);
        ptemp=ptemp->pnext;

    }
}

Answer 2

看着你的代码，在我看来，在函数addList_II中你应该用前一行代替

adddata->pnext = head;

代替： adddata-＆gt; pnext = head-＆gt; pnext; 否则你总会丢失一个元素。然后，您只需设置head=NULL，而不是初始化列表。

为什么我在C中的链表失败了？

2 个答案: