Question

我正在上C课，其中一项任务是创建一个数据库。现在，我尝试将我提供的一些输入添加到列表中，但是我一直遇到分段错误。我在做什么错了？

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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。

edit：感谢所有回答，我弄清楚了如何使用GDB。现在，原始问题已解决，我遇到了相同的错误，但是这次似乎是“ tempcar2”：

#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);
}

Answer 1

我在gdb中运行了您的程序，它指向第52行

Program received signal SIGSEGV, Segmentation fault.
0x00000000004007b6 in addCarinfo (carbase=0x0, newcar=0x602010) at so.c:52
(gdb) bt 
#0  0x00000000004007b6 in addCarinfo (carbase=0x0, newcar=0x602010) at so.c:52
#1  0x00000000004008e7 in main () at so.c:89

这是它的错误，而不是==您在使用=。

// Your assigning carbase struct pointer to NULL instead of validating pointer is null. 
    if(carbase=NULL){ //change to carbase == NULL
        carbase = newcar;
        return carbase;
    }

如何使用GDB进行调试：

如果使用gcc，则使用-g标志编译C代码。示例：gcc -g file.c
gdb ./a.out
bt（回溯，如果会指出调用堆栈）

Answer 2

代码中的一些问题：

某些变量未初始化（例如tempcar2，这是全局变量）
某些局部变量和全局变量具有相同的名称
使用=而不是==运算符进行一些比较
在打印功能中，始终打印carbase而不是tempprint
malloc返回，it should not

编译器可能已检测到某些问题：开启编译器警告（对于大多数编译器，-Wall）

在编译带有警告的代码时，您的问题就会显示出来：

.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;       
}

使用此代码的结果是：

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

制作链表时出现分段错误（核心转储）错误

2 个答案: