尝试使用双指针结构读取 csv 文件并打印出条目，但我在 C 中收到“大小为 8 的无效读取”

Question

Creating a C program to read a csv file into a double pointer struct but I'm getting a segmentation fault.

This is the struct:

typedef struct vehicle{
char *make;
char *model;
char *color;
char *license_plate;
int year;
}vehicle_t;

I'm using a single pointer and double pointer in this program to get a better understanding of using pointers:

vehicle_t *v = NULL;
vehicle_t **car;
car = calloc(1, sizeof(vehicle_t *));
int num_cars = 0;

while(!fgets(buffer, BUF_SIZE, fp)){
  //car = calloc(1, sizeof(vehicle_t *));
  *(car+num_cars) = calloc(1, sizeof(vehicle_t));
  *((car)+num_cars) = read_csv(fp, v);
  num_cars++;

  //free(v->year);
  free(v->make);
  free(v->model);
  free(v->color);
  free(v->license_plate);
  free(v);
}

Here is the function I created to read csv file and return that in car:

vehicle_t *read_csv(FILE *fp, vehicle_t *v){
char buffer[BUF_SIZE] = {0};
    v = calloc(1, sizeof(vehicle_t));
    fgets(buffer, BUF_SIZE, fp);
        char *tok = strtok(buffer, ",");
        (v)->year = atoi(tok);
        tok = strtok(NULL, ",");
        (v)->make = calloc(strlen(tok)+1, sizeof(char));
        tok = strtok(NULL, ",");
        strcpy((v)->make, tok);
        (v)->model = calloc(strlen(tok)+1, sizeof(char));
        strcpy((v)->model, tok);
        tok = strtok(NULL, ",");
        (v)->color = calloc(strlen(tok)+1, sizeof(char));
        strcpy((v)->color, tok);
        tok = strtok(NULL, ",");
        (v)->license_plate = calloc(strlen(tok)+1, sizeof(char));
        strcpy((v)->license_plate, tok);

    return v;
   }

Valgrind is telling me that I'm getting an issue here when I try to print the vehicles from double pointer car:

for(int i= 0; i<=num_cars; i++){
    printf("%d %s %s (%s) LIC:%s\n", ((*car)->year), ((*car)->make), ((*car)-   >model), ((*car)->color), ((*car)->license_plate));
}

Valgrind error message:

I finish off the code by freeing the car double pointer:

for(int i= 0; i<=num_cars; i++){
  //free((*car)->year);
  free((*car)->make);
  free((*car)->model);
  free((*car)->color);
  free((*car)->license_plate);
  free(*car);
  free(car);
}

Not sure as to why I'm getting the segmentation fault. Thought I had a decent handle of pointer usage and appeared like allocated and deallocated memory correctly.

Answer 1

At least these problems:

Wrong pointer

(v)->make = calloc(strlen(tok)+1, sizeof(char));
tok = strtok(NULL, ",");  // ????
strcpy((v)->make, tok);

Code is strange. Why allocate to a string length and then change tok before copying?

I'd expect something more like

(v)->make = calloc(strlen(tok)+1, sizeof(char));
strcpy((v)->make, tok);
tok = strtok(NULL, ",");

---

Research strdup() for alternative code.

Only 1 car, wrong fgets() usage

Code only allocates for 1 car

//vehicle_t **car;
//car = calloc(1, sizeof(vehicle_t *));
//int num_cars = 0;

//while(!fgets(buffer, BUF_SIZE, fp)){
//  *(car+num_cars) = calloc(1, sizeof(vehicle_t));
//  *((car)+num_cars) = read_csv(fp, v);

int car_n = 1000;
//                       n cars 
vehicle_t **car = calloc(car_n, sizeof *car);
int num_cars = 0;

//                        v --- no !
while(num_cars < car_n &&  fgets(buffer, BUF_SIZE, fp)){
  car[num_cars] = calloc(1, sizeof car[num_cars][0]);
  car[num_cars] = read_csv(fp, v);