c - 不确定堆分配创建的未初始化值在哪里

Question

一切似乎都工作正常，内存正在分配和释放并做它应该做的事情但是当我用 valgrind --track-origins=yes 检查它时，我在输入名称和数字后得到这个条件跳转.

==25590== Conditional jump or move depends on uninitialised value(s)
==25590==    at 0x4007BD: add_car (in /students/5/gmi6y5/cs2050/lab4/a.out)
==25590==    by 0x400704: main (in /students/5/gmi6y5/cs2050/lab4/a.out)
==25590==  Uninitialised value was created by a heap allocation
==25590==    at 0x4A069EE: malloc (vg_replace_malloc.c:270)
==25590==    by 0x4006D9: main (in /students/5/gmi6y5/cs2050/lab4/a.out)

typedef struct FreightCars_
{
    char *name;
    int number;
    struct FreightCars_ *next_car;
}FreightCar;


int main(int argc, char *argv[])
{
    if(argc != 2)
    {
            printf("Insufficient number of arguements\n");
            return 0;
    }

    int size = atoi(argv[1]);
    FreightCar *engine = (FreightCar*)malloc(sizeof(FreightCar));
    int i;
    for(i=0;i<size;i++)
    {
            printf("Enter in freight car name and number: ");
            add_car(engine);
    }
    free_cars(engine);

 return 0;
}

void add_car(FreightCar *engine)
{
    FreightCar *newPtr = (FreightCar*)malloc(sizeof(FreightCar));
    newPtr->name = malloc(sizeof(char) * MAX_STR_LEN);

    if(newPtr == NULL)   
    {
            printf("Unable to allocate memory\n");
            exit(1);
    }
    scanf("%s", newPtr->name);
    scanf("%d", &newPtr->number);
    newPtr->next_car = NULL;

    if(engine->next_car == NULL)
    {
            engine->next_car = newPtr;
            printf("added at the beginning\n");     
    }
    else
    {
            FreightCar *currentPtr = engine;
            while(currentPtr->next_car != NULL)
            {
                    currentPtr = currentPtr->next_car;
            }
            currentPtr->next_car = newPtr;
            printf("added later\n");
    }
    free(newPtr->name);
}

void free_cars(FreightCar *engine)
{
    if(engine == NULL)
    {
            printf("Linked list is empty now\n");
    }
    else
    {
            free_cars(engine->next_car);
    }
    free(engine);
    engine = NULL;
}

Answer 1

主要是你做的

FreightCar *engine = (FreightCar*)malloc(sizeof(FreightCar));

然后在你调用的for循环中

        add_car(engine);

add_car 做

if(engine->next_car == NULL)

但正如@Oli Charlesworth 在评论中指出的那样，您尚未初始化引擎指向的内存，因此您正在根据此处未初始化的内存内容做出决定，因此出现了 Valgrind 投诉。