c - 制作链表时出现Segmentation fault (core dumped)错误

Question

我正在为学校学习 C，其中一项作业是创建数据库。现在我试图将我给它的一些输入添加到列表中，但我不断收到段错误。我做错了什么？

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

struct carinfo_t {
    char* carbrand;
    char* carmodel;
    int caryear;
    float carvalue;
    struct carinfo_t * next;
};

struct carinfo_t * carbase;

struct carinfo_t * tempcar;

struct carinfo_t * tempcar2;

struct carinfo_t * tempprint;

void freeCarinfo(struct carinfo_t * carinfo){
    free(carinfo->carbrand);
    free(carinfo->carmodel);
    free(carinfo);    
}

struct carinfo_t * createCarinfo(char *carbrand, char *carmodel, int caryear, float carvalue){
    struct carinfo_t * newcar;
    newcar = (struct carinfo_t *)malloc(sizeof (struct carinfo_t));
    newcar->carbrand=(char *)malloc(sizeof(char)*(strlen(carbrand) + 1));
    strcpy(newcar->carbrand, carbrand);

    newcar->carmodel=(char *)malloc(sizeof(char)*(strlen(carmodel) + 1));
    strcpy(newcar->carmodel, carmodel);

    newcar->caryear=caryear;

    newcar->carvalue=carvalue;

    newcar->next= NULL;

    return newcar;
}

struct carinfo_t * addCarinfo(struct carinfo_t *carbase, struct carinfo_t *newcar){
    if(carbase=NULL){
        carbase = newcar;
        return carbase;
    }

    else{
        tempcar2->next=carbase;
        carbase=tempcar2;
        return carbase;

    }

}

void printCarbase(struct carinfo_t *carbase){

    struct carinfo_t *tempprint = carbase;

    if (carbase == NULL){
        printf("The database contains no cars\n");
    }

    else{
        while (tempprint != NULL){
            printf("Car:\n");
            printf("- brand: %s\n", carbase->carbrand);
            printf("- model: %s\n", carbase->carmodel);
            printf("- year: %d\n", carbase->caryear);
            printf("- value: %7.2f\n", carbase->carvalue);
            tempprint = tempprint->next;
        }
    }
}


void main(void){
    struct carinfo_t * carbase;
    carbase = NULL;

    struct carinfo_t * tempcar;
    tempcar = createCarinfo("Opel", "Manta", 1965, 20000);

    struct carinfo_t * tempcar2 = createCarinfo("Ford", "Focus", 1999, 350.25);
    addCarinfo(carbase, tempcar);
}

此外，如果您发现任何改进我的代码的方法，请告诉我，我是编程的新手，我希望能够正确地做到这一点。

编辑:感谢所有回复的人，我弄清楚了如何使用 GDB。现在原来的问题已经解决了，我得到了同样的错误，但这次似乎是“tempcar2”的问题:

Program received signal SIGSEGV, Segmentation fault.
0x000000000040072a in addCarinfo (carbase=0x602010, newcar=0x602080)
    at database.c:56
56              tempcar2 = tempcar2->next;
(gdb) bt
#0  0x000000000040072a in addCarinfo (carbase=0x602010, newcar=0x602080)
    at database.c:56
#1  0x0000000000400869 in main () at database.c:98

Answer 1

代码中的一些问题:

• 一些变量没有被初始化(例如tempcar2，它是全局的)
• 一些局部变量和全局变量同名
• 一些比较是用 = 而不是 == 运算符完成的
• 在你的 print 函数中，你总是打印 carbase 而不是 tempprint
• malloc 返回被强制转换，it should not

编译器可能已经检测到一些问题:打开编译器警告(-Wall 对于大多数编译器)

当你的代码编译时带有警告，你的问题就会暴露出来:

.code.tio.c: In function ‘addCarinfo’:
.code.tio.c:46:8: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
     if(carbase=NULL){
        ^~~~~~~
.code.tio.c: At top level:
.code.tio.c:81:6: warning: return type of ‘main’ is not ‘int’ [-Wmain]
 void main(void){
      ^~~~
.code.tio.c: In function ‘main’:
.code.tio.c:88:24: warning: unused variable ‘tempcar2’ [-Wunused-variable]
    struct carinfo_t * tempcar2 = createCarinfo("Ford", "Focus", 1999, 350.25);
                        ^~~~~~~~

更正后的版本可能是:

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

struct carinfo_t
{
    char* carbrand;
    char* carmodel;
    int caryear;
    float carvalue;
    struct carinfo_t * next;
};

void freeCarinfo(struct carinfo_t * carinfo)
{
    free(carinfo->carbrand);
    free(carinfo->carmodel);
    free(carinfo);    
}

struct carinfo_t * createCarinfo(char *carbrand, char *carmodel, int caryear, float carvalue)
{
    struct carinfo_t * newcar;
    /* malloc cast is not recommender */
    newcar = malloc(sizeof (struct carinfo_t));

    /* strdup can be used here */
    newcar->carbrand = strdup(carbrand);    
    newcar->carmodel = strdup(carmodel);

    newcar->caryear=caryear;
    newcar->carvalue=carvalue;

    newcar->next= NULL;

    return newcar;
}

struct carinfo_t * addCarinfo(struct carinfo_t *carbase, struct carinfo_t *newcar)
{
    if(carbase==NULL)
    {
        carbase = newcar;
        return carbase;
    }
    else
    {
        /* find for the last element */
        struct carinfo_t * tempcar2 = carbase;
        while(tempcar2->next)
        {
            tempcar2 = tempcar2->next;
        }
        /* add the new car to the list */
        tempcar2->next=newcar;

        return carbase;
    }
}

void printCarbase(struct carinfo_t *carbase)
{
    struct carinfo_t *tempprint = carbase;

    if (carbase == NULL)
    {
        printf("The database contains no cars\n");
    }
    else
    {
        while (tempprint != NULL)
        {
            printf("Car:\n");
            printf("- brand: %s\n", tempprint->carbrand);
            printf("- model: %s\n", tempprint->carmodel);
            printf("- year: %d\n", tempprint->caryear);
            printf("- value: %7.2f\n", tempprint->carvalue);
            tempprint = tempprint->next;
        }
    }
}

int main(void)
{
   struct carinfo_t * carbase;
   carbase = NULL;

   struct carinfo_t * tempcar;
   tempcar = createCarinfo("Opel", "Manta", 1965, 20000);

   struct carinfo_t * tempcar2 = createCarinfo("Ford", "Focus", 1999, 350.25);
   carbase = addCarinfo(carbase, tempcar);
   carbase = addCarinfo(carbase, tempcar2);
   printCarbase(carbase);

   return 0;       
}

这段代码的结果是:

Car: 
- brand: Opel
- model: Manta
- year: 1965
- value: 20000.00
Car: 
- brand: Ford
- model: Focus
- year: 1999
- value:  350.25