(Read from file) Linked list in C - c

Question

I'm new to C programming, and I'm having some difficulties. I'm trying to re-code to use a linked list to store the structs you read from the file, but I can't understand how to save the text line for line and add it to the linked list.
This is my code:
#include<stdio.h>
#include<stdlib.h>
#include"Cars.h"
void write_to_file() {
FILE* file = NULL;
file = fopen("Cars.dat", "wb");
Car c = { "Toyota", "Civic", "black", 5, 50000 };
size_t ret = fwrite(&c, sizeof c, 1, file);
Car d = { "Toyota1", "Civic1", "Red", 2, 55000 };
ret = fwrite(&d, sizeof d, 1, file);
fclose(file);
}
void print_cars(Car *c, int count) {
FILE* f = fopen("output.txt", "w");
for (int i = 0; i < count; i++) {
fprintf(f, "%s %s %s %d %f\n", c[i].model, c[i].manufacturer, c[i].color, c[i].seatCapacity, c[i].price);
}
fclose(f);
}
void read_from_file() {
Car c;
size_t SIZE = sizeof c;
size_t ret = 1;
FILE* file = NULL;
file = fopen("Cars.dat", "rb");
int count = 0;
do{
ret = fread(&c, sizeof c, 1, file);
if (ret != 1)
break;
count++;
//printf("%s %s %s %d %f\n", c.model, c.manufacturer, c.color, c.seatCapacity, c.price);
}while(!feof(file));
fclose(file);
if (count == 0) {
printf("No cars in the file provided\n");
return;
}
file = fopen("Cars.dat", "rb");
Car* cars_array = NULL;
cars_array = (Car *)malloc(count * SIZE);
ret = fread(cars_array, SIZE*count, 1, file);
//printf("%d\n", ret);
print_cars(cars_array, count);
}
int main()
{
//write_to_file();
read_from_file();
return 0;
}
Struct code:
#ifndef Cars_h
#define Cars_h
typedef struct cars {
char manufacturer[35]; //toyota, honda
char model[35]; //camry, civic
char color[20]; //black, red
int seatCapacity; //4,5
float price; //20k, 25k
}
Car;
#endif
If anyone could give me some pointers on what I need to do next to make it work, I would highly appreciate it. Thank you

Answer 1

You could implement a linked list of 'Car' objects by adding a next pointer to the Car structure. For example:
typedef struct Car {
/* existing fields */
char model[LLL];
char manufacturer[MMM];
char color[CCC];
int seatCapacity;
float price;
struct Car *next; /* new member for linked list */
} Car;
(An assumption is made about Car as source code for Cars.h was not provided.)
You would have to account for this extra field in Cars.dat (where it could be stored with a NULL value assuming that the file has just an array and no notion of a linked list).
When reading, you could malloc space for each Car separately, fread it into the malloc-ed buffer, and update the previous' Car's next pointer to point to the newly loaded Car. In this manner you can build up a simple linked list of Cars.
p.s. I've never heard of a Toyota Civic :)

Answer 2

You can create a new struct as below which includes your Car struct as a field. And a pointer to the next node.
typedef struct {
Car payload;
CarNode* nextNode;
}CarNode
And you don't need to calculate the count of records in the file. Just read one and malloc a CarNode and use the CarNode.payload field as the buffer to hold the content read from the file. Something like below snippet:
CarNode head, tail; // Suppose you are using single linked list.
/*
Initialize the head and tail pointer. At first, they should both point to the first node.
*/
...
/*
Allocate a new node while reading a record from the file.
*/
CarNode *p = (CarNode *)malloc(sizeof(CarNode));
ret = fread(&(p->payload), sizeof(Car), 1, file);
/*
Insert the newly read node into the link list.
*/
tail->nextNode = p;
tail = p;